She is then expected to deliver a farewell speech at 10.15am as her time as the shortest-serving leader in British history draws to a close.
Ms Truss will then travel to Buckingham Palace for her final audience with King Charles.
It will then be Mr Sunak’s turn to go to the palace, and the monarch will invite him to form the next government.
After officially being appointed as prime minister, the new Conservative Party leader is expected to then travel back to Downing Street.
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He will then make a public address on the steps of Number 10 at about 11.35am.
Mr Sunak won the leadership raceyesterday after Penny Mordaunt bowed out at the eleventh hour – having failed to get the 100 nominations from Tory MPs required by the 2pm deadline.
Sources in the Mordaunt camp said she got 90 nominations, though the number of those who publicly announced their backing of her fell far short of this.
“We all owe it to the country to each other and to Rishi to unite and work together for the good of the nation. There is much work to be done,” Ms Mordaunt said in a tweet.
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Mr Sunak is the UK’s first Hindu prime minister, the first of Asian heritage, and the youngest for more than 200 years at the age of 42.
The title of youngest ever prime minister belongs to William Pitt the Younger, who was just 24 when he took office in 1783. Tony Blair was 43.
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6:39
Three PMs in three months: A timeline
In his first comments after winning the contest, Mr Sunak said he was “humbled and honoured” that Tory MPs had chosen him to lead the party and the nation – describing it as the “greatest privilege in my life”.
Mr Sunak also paid tribute to outgoing prime minister Liz Truss for her “dedicated public service” in a brief speech at the Conservative Party headquarters in Westminster.
“The United Kingdom is a great country, but there is no doubt we face a profound economic challenge,” he said.
“We now need stability and unity, and I will make it my utmost priority to bring our party and our country together.”
Worldwide stock markets have plummeted for the second day running as the fallout from Donald Trump’s global tariffs continues.
While European and Asian markets suffered notable falls, American indexes were the worst hit, with Wall Street closing to a sea of red on Friday following Thursday’s rout – the worst day in US markets since the COVID-19 pandemic.
All three of the US’s major indexes were down by more than 5% at market close; The Dow Jones Industrial Average plummeted 5.5%, the S&P 500 was 5.97% lower, and the Nasdaq Composite slipped 5.82%.
The Nasdaq was also 22% below its record-high set in December, which indicates a bear market.
Ever since the US president announced the tariffs on Wednesday evening, analysts estimate that around $4.9trn (£3.8trn) has been wiped off the value of the global stock market.
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Mr Trump has remained unapologetic as the markets struggle, posting in all-caps on Truth Social before the markets closed that “only the weak will fail”.
The UK’s leading stock market, the FTSE 100, also suffered its worst daily drop in more than five years, closing 4.95% down, a level not seen since March 2020.
And the Japanese exchange Nikkei 225 dropped by 2.75% at end of trading, down 20% from its recent peak in July last year.
Image: US indexes had the worst day of trading since the COVID-19 pandemic. Pic: Reuters
Trump holds trade deal talks – reports
It comes as a source told CNN that Mr Trump has been in discussions with Vietnamese, Indianand Israelirepresentatives to negotiate bespoke trade deals that could alleviate proposed tariffs on those countries before a deadline next week.
The source told the US broadcaster the talks were being held in advance of the reciprocal levies going into effect next week.
Vietnam faced one of the highest reciprocal tariffs announced by the US president this week, with 46% rates on imports. Israeli imports face a 17% rate, and Indian goods will be subject to 26% tariffs.
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China – hit with 34% tariffs on imported goods – has also announced it will issue its own levy of the same rate on US imports.
Mr Trump said China “played it wrong” and “panicked – the one thing they cannot afford to do” in another all-caps Truth Social post earlier on Friday.
Later, on Air Force One, the US president told reporters that “the beauty” of the tariffs is that they allow for negotiations, referencing talks with Chinese company ByteDance on the sale of social media app TikTok.
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6:50
Tariffs: Xi hits back at Trump
He said: “We have a situation with TikTok where China will probably say, ‘We’ll approve a deal, but will you do something on the tariffs?’
“The tariffs give us great power to negotiate. They always have.”
Global financial markets gave a clear vote of no-confidence in President Trump’s economic policy.
The damage it will do is obvious: costs for companies will rise, hitting their earnings.
The consequences will ripple throughout the global economy, with economists now raising their expectations for a recession, not only in the US, but across the world.
The court ruled to uphold the impeachment saying the conservative leader “violated his duty as commander-in-chief by mobilising troops” when he declared martial law.
The president was also said to have taken actions “beyond the powers provided in the constitution”.
Image: Demonstrators stayed overnight near the constitutional court. Pic: AP
Supporters and opponents of the president gathered in their thousands in central Seoul as they awaited the ruling.
The 64-year-old shocked MPs, the public and international allies in early December when he declared martial law, meaning all existing laws regarding civilians were suspended in place of military law.
Image: The court was under heavy police security guard ahead of the announcement. Pic: AP
After suddenly declaring martial law, Mr Yoon sent hundreds of soldiers and police officers to the National Assembly.
He has argued that he sought to maintain order, but some senior military and police officers sent there have told hearings and investigators that Mr Yoon ordered them to drag out politicians to prevent an assembly vote on his decree.
His presidential powers were suspended when the opposition-dominated assembly voted to impeach him on 14 December, accusing him of rebellion.
The unanimous verdict to uphold parliament’s impeachment and remove Mr Yoon from office required the support of at least six of the court’s eight justices.
South Korea must hold a national election within two months to find a new leader.
Lee Jae-myung, leader of the main liberal opposition Democratic Party, is the early favourite to become the country’s next president, according to surveys.