Boris Johnson is fighting for political survival after two of his top ministers attacked his leadership and resigned.
Chancellor Rishi Sunak and Health Secretary Sajid Javid quit within 10 minutes of each other, followed by a flurry of junior ministers and aides.
In his resignation letter, Mr Sunak said the public “rightly expect integrity from their government”.
But new chancellor Nadhim Zahawi urged his colleagues to unite and said Mr Johnson was focused on delivery.
Mr Zahawi, who becomes the fourth chancellor in three years, was appointed alongside the prime minister’s chief of staff, Steve Barclay, who became health secretary.
A No 10 source said the new chancellor was “more dynamic and more aligned” with Mr Johnson, and described the new health secretary as a “massive upgrade”.
Later on Wednesday, Mr Johnson will come under further pressure when he faces MPs at Prime Minister’s Questions.
He is also due to give evidence to the Liaison Committee – a group of MPs who scrutinise the government’s policy and decisions.
Bim Afolami – who quit as vice-chair of the party live on TV on Tuesday evening – said Downing Street’s handling of the Chris Pincher affair had been “really appalling” and he could no longer “defend that sort of behaviour”.
He told BBC Radio 4’s Today programme he supported Mr Johnson in his recent confidence vote in order to give him time to rebuild trust after Partygate, but things had “got a lot worse” in recent weeks.
Neither Mr Javid nor Mr Sunak have publicly spoken since standing down, but their resignation letters on Tuesday were highly critical of the PM.
Mr Javid warned the leadership was not “acting in the national interest”, while Mr Sunak said the public expected government to be conducted “properly, competently and seriously”.
Opposition party leaders urged cabinet ministers to join the pair and resign, and Labour leader Sir Keir Starmer said he was ready for a snap general election.
Conservative MP and former chief whip, Andrew Mitchell, told BBC Newsnight it was “over” for Mr Johnson, saying “he has neither the character nor the temperament to be our prime minister” – and the only question was how long the affair would go on.
But no Tory MPs have declared a leadership challenge against the prime minister and several ministers have rallied around the PM, including Foreign Secretary Liz Truss – one potential contender to replace him as Tory leader.
She said she was “100% behind the PM”, while cabinet ministers including Dominic Raab, Michael Gove, Therese Coffey and Ben Wallace also indicated they would be staying in the government.
Tory backbencher Daniel Kawczynski suggested the resignations would ultimately strengthen Mr Johnson’s position, adding they “could have triggered an avalanche against the prime minister but it hasn’t”.