Power supplies have been returning in Spain and Portugal after large parts, including the capitals Madrid and Lisbon, were hit by a huge outage on Monday.

Millions of people were caught up in the chaos after the mass blackout brought many areas to a standstill, with trains stopping, planes grounded, internet and mobile phone services cut, traffic lights and ATMs down, and some routine hospital operations suspended.

Spain‘s interior ministry declared a national emergency and the two countries’ governments convened emergency cabinet meetings as officials tried to find out what caused the outage which started around 12.30pm (11.30am UK time).

Blackouts in Spain and Portugal: Follow latest updates

About half the electricity supplies in Spain have now been restored by the grid operator, Prime Minister Pedro Sanchez said on Monday evening, adding the rest should be back by Tuesday.

In a televised address, Mr Sanchez said authorities have not yet worked out what had caused the blackout in the Iberian Peninsula and were not ruling anything out.

He asked the public to refrain from speculation, and urged people to call emergency services only if really necessary.

Eduardo Prieto, the head of operations at Spanish power grid operator Red Electrica, said the event was unprecedented, calling it “exceptional and extraordinary”.

Meanwhile, Portugal‘s Prime Minister Luis Montenegro said power in his country would be fully restored in the coming hours.

He said all the state services remained operating in the country despite all the difficulties. He also said there was “no indication” a cyberattack was the cause.

Read more: Analysis – How electricity grids fail

‘Rare atmospheric phenomenon’

Portugal’s grid operator Ren claimed the outage was caused by a fault in the Spanish electricity grid, related to a “rare atmospheric phenomenon”.

Ren says that, due to extreme temperature variations in Spain, there were “anomalous oscillations” in very high-voltage lines.

It also says that given the complexity of the issue, it could take up to a week for the network to fully normalise again.

It comes as France briefly lost power following the outages in Spain and Portugal, French grid operator RTE said.

Parts of Madrid underground were evacuated and traffic lights in the city were not working, according to local media.

Play was suspended at the Madrid Open tennis tournament due to the outage – with Britain’s Jacob Fearnley forced off court in a critical moment during his third-round tie with Grigor Dimitrov.

The loss of power affected scoreboards and the camera above the court. Organisers later announced the tournament would not be able to resume on Monday, with afternoon and evening sessions cancelled.

Airports affected

Aena, which runs international airports across Spain, said earlier that “some incidents were occurring” at the airports due to the outage.

The company added in a statement: “Contingency generators are active. Please check with your airline, as there may be disruptions to access and ground transportation.”

People ‘had nowhere to go’

Maddie Sephton, who is from west London, was on the Madrid Metro when the power outage occurred.

“We got on the train and everything was fine,” she told Sky News. “But then everything went dark.”

She was stuck on the train for 20 minutes until a staff member opened the doors manually.

Mrs Sephton says she was on her way to the airport at the time – and had to exit the station by walking up 15 flights of stairs with her luggage.

“No lifts are operating – making it difficult for elderly people with limited mobility,” she added.

Above ground, she said that “everyone is just standing around and waiting”.

Bars were unable to take card payments, cash machines are down, and traffic lights weren’t working either.

“I currently don’t have any internet service and just €15 in my wallet – I can’t withdraw any money from the ATM,” she added.

“A couple have offered to let us get a ride in their taxi to the airport. Their flight is at 4.30pm so they’re pretty relaxed – but my flight back to London is at 3pm and I’m nervous.”

Mrs Sephton said: “People are just walking but have nowhere to go, and nothing to do.”

Meanwhile, thousands of passengers had to be evacuated after the blackout left the metro service in Barcelona without power.

The blackout was also reported to have forced the closure of the city’s tram system and rendered some traffic lights there inoperable.

It has also impacted medical facilities, with hospitals in Madrid and Catalonia forced to suspend routine medical work. Staff have been able to attend to critical patients using power from backup generators.

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It comes as Metrovalencia, the urban rail system, encompassing both metro and tram services in Valencia, said traffic in the city was “disrupted” due to a “general power outage in the city”.

The outage also hit the Portuguese capital Lisbon and surrounding areas, as well as northern and southern parts of the country.

Portugal’s government said the incident appeared to stem from problems outside the country, an official told national news agency Lusa.

“It looks like it was a problem with the distribution network, apparently in Spain. It’s still being ascertained,” Cabinet Minister Leitão Amaro was quoted as saying.

We rarely think about how essential and reliable electricity grids are until they fail.

Now, millions of people across Spain, Portugal and parts of France are likely thinking of little else.

While local power cuts are fairly common, what’s happened across the Iberian peninsula is something far more extreme.

Much of Spain and Portugal’s electricity transmission system collapsed in seconds including in major cities Lisbon, Madrid, Barcelona and Seville.

Blackouts latest: ‘Rare atmospheric phenomenon’ behind outages

It’s likely the outage will surpass Europe’s largest blackout to date when 56 million people in Italy and Switzerland lost power for up to 12 hours in 2023.

The cause of the outage is unclear. Portugal’s grid operator has blamed a “rare atmospheric phenomenon” that caused “anomalous oscillations” in high voltage power lines in Spain.

Spain’s grid operator has yet to respond to that or provide an update on the cause. But it’s unlikely whatever caused the outage was a single, localised event.

A major power line going down can cause a large outage – as it did in 2021, when an interconnector between France and Spain failed leaving a million people without power for a few hours.

But it’s unlikely to cause a system-wide failure of the kind we’re seeing now.

However, when things do start to fail on a power grid, they can cascade uncontrollably.

Keeping a grid running is a constant and highly complex balancing act.

Spain’s mains AC electricity supply grid, like ours in the UK, runs at 50Hz. That frequency is based on the speed at which generating hardware such as gas and nuclear turbines spin.

If there are sudden fluctuations in power supply or demand – a power station failing or a high voltage power line going down, for example – the frequency of AC power in the transmission lines changes and circuit breakers trip to protect either the transmission network, or power plant hardware from burning out.

To prevent such failures, grid engineers constantly measure and forecast supply and demand to keep the grid balanced.

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To protect the system in emergencies, they occasionally have to “shed load” by cutting power to parts of the grid – the reason we’ve all experienced the occasional short-lived power cut.

But if balance is lost, a grid can fail in a domino effect with sections of the grid tripping, then power plants shutting down to protect themselves from the drop in demand, one after another.

The challenge now, and it’s a nightmare for Spain and Portugal’s power engineers, is to gradually restore the grid section by section while maintaining the balance of supply and demand.

Act too fast, and the grid can trip again. Take too long and some power plants or substations might struggle to restart – especially if they rely on battery power to do so.

While some regions of Spain have already had power restored, and Portugal says its power will be back to normal within hours, it could take much longer for the system to be fully restored.

A Palestinian diplomat has told the United Nations’ top court that Israel is “starving, killing and displacing” civilians and targeting aid workers in Gaza.

Israel denies deliberately targeting civilians and aid staff and did not attend the hearing at the International Court of Justice (ICJ) on Monday.

At The Hague, Palestinian ambassador to the Netherlands, Ammar Hijazi, accused Israel of breaching international law in the occupied territories.

He said: “Israel is starving, killing and displacing Palestinians while also targeting and blocking humanitarian organisations trying to save their lives.”

The hearings are focused on a request last year from the UN General Assembly, which asked the court to weigh in on Israel’s legal responsibilities after the country blocked the United Nations Relief and Works Agency (UNRWA) for Palestine refugees from operating on its territory.

In a resolution sponsored by Norway, the General Assembly requested an advisory opinion, a non-binding but legally important decision from the court, on Israel’s obligations in the occupied territories to “ensure and facilitate the unhindered provision of urgently needed supplies essential to the survival of the Palestinian civilian population”.

While Israel was not in court, foreign minister Gideon Saar told a news conference in Jerusalem: “I accuse UNRWA, I accuse the UN, I accuse the secretary-general and I accuse all those that weaponised international law and its institutions in order to deprive the most attacked country in the world, Israel, of its most basic right to defend itself.”

Forty states and four international organisations are scheduled to participate in the ICJ hearings, with it likely taking months for the court to rule.

The hearings come amid the near collapse of the humanitarian aid system in Gaza.

Israel has blocked the entry of food, fuel, medicine and other humanitarian supplies since 2 March.

The World Food Programme said last week its food stocks in the Gaza Strip had run out.

Israel also renewed its bombardment on 18 March, breaking a ceasefire, and seized large parts of the territory, claiming it aims to push Hamas to release more hostages.

Overnight into Monday, at least 27 Palestinians were killed in Israeli strikes, according to local health officials.

An air strike hit a home in Beit Lahia, killing 10 people, including a Palestinian prisoner, Abdel-Fattah Abu Mahadi, who had been released as part of the ceasefire.

His wife, two of their children and a grandchild were also killed, according to Indonesia Hospital which received the bodies.

Another strike hit a home in Gaza City, killing seven people, according to the Gaza Health Ministry’s emergency service.

And late on Sunday, a strike hit a home in the southern city of Khan Younis, killing at least 10 people, including five siblings as young as four-years-old, according to the health ministry.

Two other children were killed along with their parents, according to Nasser Hospital which received the bodies.

There was no immediate comment from the Israeli military.

Israel claims it makes every effort to avoid harming civilians and blames Hamas for their deaths because the militants operate in densely populated areas.

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Israel’s ban on UNRWA came into effect in January.

The organisation has faced increased criticism from Prime Minister Benjamin Netanyahu and his far-right allies, who claim the group is deeply infiltrated by Hamas, which UNRWA refutes.

Amir Weissbrod, a foreign ministry official, presented Israel’s case against UNRWA on Monday.

He accused it of failing to act before the war against evidence that Hamas had used its facilities, including by digging tunnels underneath them.

The official said UNRWA employed 1,400 Palestinians with militant ties.

Israel claims some of those employees also took part in Hamas’ attacks on 7 October 2023, with at least three of those employees still allegedly working for the UN.

The presentation included videos, documents and pictures of the alleged employees.

The 7 October 2023 attack in southern Israel killed around 1,200 people and prompted the ongoing Israeli offensive in Gaza – which the territory’s health ministry says has killed more than 52,000 people.

UNRWA said it fired nine staffers after an internal UN investigation concluded that they could have been involved, although the evidence was not authenticated and corroborated.

The ban does not apply directly to Gaza, but UNRWA is prohibited from operating inside Israel which affects the agency’s ability to function.

Israeli officials claim they are looking for alternative ways to deliver aid to Gaza that would cut out the UN.