Officers were then called to Milton Street, in the city centre, where a driver had tried to run over people in a van. One person is in a critical condition, two others have minor injuries.
The man in his fifties was found dead with knife injuries by a member of the public in nearby Magdala Road.
The University of Nottingham said it was “shocked and devastated” as it revealed two of its students were among the dead.
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Footage appears to show man being arrested
Police have arrested a 31-year-old man on suspicion of murder and he remains in custody.
Video appears to show him on the ground next to the van as officers detained him.
Photos of the vehicle show small cracks on the windscreen and apparent damage to the bumper.
Chief Constable Kate Meynell said they believe it was stolen from the middle-aged victim and used to drive at members of the public.
Image: Forensics officers on Ilkeston Road
Police are working alongside specialist terror officers, but say they are keeping an “open mind” over the motive and are not looking for anyone else.
Hours after the attacks, at around 12.30pm, there was a “flurry of activity” as armed police cut off Ilkeston Road – where the students were stabbed, said Sky correspondent Becky Johnson.
She said two young women were put in the back of a marked car after officers appeared to enter a commercial property.
Chief Constable Meynell later said a number of searches had been carried out across the city but no further arrests.
Pair ‘stabbed by attacker in black’
A witness told the BBC he saw a man and woman being stabbed on Ilkeston Road at around 4am.
He said he heard “awful, blood-curdling screams” and there was a “black guy dressed all in black with a hood and rucksack grappling with some people”.
He said the woman was shouting for help.
“I saw him stab the lad first and then the woman. It was repeated stabbing – four or five times. The lad collapsed in the middle of the road,” the witness said.
“The girl stumbled towards a house and didn’t move. The next minute she had disappeared down the side of a house, and that’s where they found her.
“I’d say it all happened within five or six minutes. The attacker then just walked off up Ilkeston Road towards town, as calm as anything.”
The man called police, who arrived in about five minutes, before paramedics tried to revive the pair for 40 minutes.
‘I saw two people on the floor’
Another witness, who gave her name as Frances, told Sky News she heard a sudden bang and screaming as a white van drove into people in the city centre.
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Suspect used victim’s van to drive at three people
She said she “crossed over the road at Theatre Royal and got around 10 feet down the road when all of a sudden you heard a bang – which sounded like a vehicle hitting a bollard”.
“I turned around and then saw the two people on the floor, on the road,” she added.
“Someone was screaming, I think a gentleman ran over to help as well.
“Then it just went from there, the police were there straight away, then the ambulance arrived and they got the two people in the ambulance and got them sent off to whichever hospital.”
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A body has been found in the search for 23-year-old runner Jenny Hall.
She was last seen leaving her home in Barracks Farm, County Durham, in her car just after 3pm on Tuesday.
Police said there are not thought to be any suspicious circumstances after a body was found in a very remote area in Teesdale on Sunday morning, five days after she went missing.
Image: Jenny Hall went missing on Tuesday. Pic: Durham Constabulary
“We’re sorry to report that officers searching for missing woman Jenny Hall, have sadly found a body,” Durham Constabulary said in a statement.
“Officers carried out an extensive search alongside specialist partners and have been working around-the-clock to locate Jenny after she went missing on February 18.
“The body was found in a very remote area in Teesdale just after 9.30am today.
“Formal identification has yet to take place. Jenny’s family have been notified and are currently being supported by specialist officers. They have asked for privacy at this devasting time.
“It is not believed there are any suspicious circumstances and a file will be prepared for the coroner.”
Her car, a red Ford Focus, was found on Wednesday parked on the B6278, near remote moorland between Eggleston and Stanhope.
Mountain rescue teams, specialist drones and sniffer dogs had been combing the Hamsterley Forest and the surrounding areas, where there are a number of running trails, this week.
Digital intelligence officers also carried out extensive inquiries into Ms Hall’s mobile phone, smart watch and running apps.
A fresh amber weather warning for heavy rain has been issued by the Met Office – with much of the UK already on alert for high winds and showers.
Northern Ireland, Scotland and the UK’s west coast and the Midlands have yellow warnings for wind on Sunday – meaning the possibility of transport delays and short-term power cuts.
There are also rain warnings in place for several parts of western UK.
The new amber warning has been issued for rain in south and central Wales and is in force from 3pm on Sunday to 6am on Monday.
An amber warning means danger to life from floodwater, homes and businesses are likely to be flooded, and there is a chance some communities will be cut off.
Winds across the west of the UK will increase throughout the morning with gusts up to 70mph in exposed areas, the Met Office said.
Zoe Hutin, a meteorologist at the forecaster, said Sunday is expected to be the “worst day” before conditions improve.
“The wind warning itself for the mainland UK ends at 6pm, but we can expect to continue to see quite blustery conditions even into the evening as the mainland rain itself pushes through.”
She added: “By the time people get up on Monday, we’ll still have some of the residual rain from that front in the far south-east of the country, and quite cloudy across England as well.
“But actually elsewhere, it could be a decent start.”
The Met Office’s yellow weather warnings for much of England and Scotland came into force at 6am and are expected to run until 6pm on Sunday.
A separate yellow warning for Northern Ireland came into force at 3am and runs until 3pm.
Image: Rain and high winds are expected across the west of the UK
Sir Keir Starmer has said the United States “is right” about the UK and Europe needing to take more responsibility for defence and security.
The prime minister, speaking at the Scottish Labour conference in Glasgow on Sunday, said he is clear Britain “will take a leading responsibility” in protecting the continent.
“Instability in Europe always washes up on our shores,” he said.
“And this is a generational moment. I’ve been saying for some time that we Europeans – including the United Kingdom – have to do more for our defence and security. The US is right about that.”
He added “we can’t cling to the comforts of the past” as it is “time to take responsibility for our security”.
Donald Trump sparked an emergency meeting of European leaders this week after he said European NATO members should spend more on defence, while the US should spend less.
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Will Trump and Starmer have a ‘Love Actually’ moment?
Sir Keir has said he will set out a path for the UK to spend 2.5% of GDP on defence, up from the current 2.3%, but has not indicated when that will be.
It is believed he may announce the details when he visits Mr Trump in Washington DC on Thursday, bringing forward the announcement that was expected in the spring when a defence spending review is published.
The prime minister reiterated the UK will “play our role” if required in Ukraine following a peace agreement after he earlier this week said the UK would send troops to be part of a peacekeeping force.
Image: Sir Keir will meet Donald Trump in the White House on Thursday. Pic: AP
However, his comments caused a row with Germany and Italy who said it was premature to commit to boots on the ground, although France agreed with the UK.
Sir Keir said: “As we enter a new phase in this conflict, we must now deepen our solidarity even further.”
He added: “There can be no discussion about Ukraine without Ukraine.
“And the people of Ukraine must have long-term security.”
No Europeans were invited either, sparking concern the US is pandering to Vladimir Putin.
Sir Keir has promised Mr Zelenskyy he will make the case for safeguarding Ukraine’s sovereignty when he meets with Mr Trump, who has called the Ukrainian president a dictator.
Mr Trump also said Sir Keir and French President Emmanuel Macron, who will visit the White House too this week, “haven’t done anything” to end the war.