Just last month Liz Truss told Britons they could “ride out the storm” in her first speech as prime minister – now she has resigned.
Here, Sky News looks at the runners and riders to replace the PM.
Live politics updates as Liz Truss resigns
The former chancellor, who was runner-up to Ms Truss in the Tory leadership race, is favourite with the bookmakers to replace her.
He warned his rival that her tax-cutting plans would send the economy into free fall, accusing her of “fairytale economics” as she promised unfunded tax cuts.
Following the fallout from the mini-budget, supporters of Mr Sunak believe he has been vindicated. One MP who supported him in the leadership race told the Telegraph: “Everything he said has come to pass.”
Mr Sunak won every voting round among MPs in the Tory leadership race but there are question marks over whether he could reunite the party, having been seen to have played a key role in Boris Johnson’s exit as PM.
The leader of the Commons finished in third place in this summer’s Tory leadership race before she backed Ms Truss’s bid.
Sky News understands Ms Mordaunt is taking soundings from colleagues on whether to stand.
The former defence secretary also caused a stir at the Tory conference earlier this month when she said the party’s “comms is s***”.
In messages shared in Conservative Party WhatsApp groups, leaked to Sky News, Tory MP Crispin Blunt called for Mr Sunak and Ms Mordaunt to take over.
“Step forward Rishi and Penny, with our support and encouragement in the interests of us all,” he wrote.
Ms Mordaunt was sent to the Commons on behalf of Ms Truss to answer an urgent question on the sacking of former chancellor Kwasi Kwarteng on Monday.
Denying that Ms Truss was hiding “under a desk”, Ms Mordaunt acknowledged the swirling rumours around the possibility of a joint ticket, telling MPs: “I fully understand the optics of me appearing at the despatch box.”
The defence secretary and former soldier is widely respected for the role he has played in the UK’s support for Ukraine.
He stayed neutral in the Tory leadership race before eventually backing Ms Truss.
There are doubts over whether he would want to be leader, having ruled himself out of this summer’s race despite being considered a frontrunner after “careful consideration and discussing with colleagues and family”.
The defence secretary told The Times on Tuesday that he wants to remain in his post amid speculation he could be a unity candidate to become PM.
Mr Wallace rebuked his Conservative colleagues for playing “political parlour games”, telling the newspaper: “The public wants stability and security and if the government fails to deliver that then they will send us into opposition.”
Asked if he wanted the keys to Number 10, he said: “I want to be the secretary of state for defence until I finish. I love the job I do and we have more to do. I want the prime minister to be the prime minister and I want to do this job.”
Mr Wallace’s only cabinet post has been defence secretary, which he has held since July 2019.
But he has signalled he would likely quit if the government ditches a key pledge to boost defence spending.
On Monday, new Chancellor Jeremy Hunt refused to commit to spending 3% of GDP on defence, telling Sky News’ political editor Beth Rigby he was “not giving any answers on any specific elements” of tax and spending policy.
In his farewell address as PM, Mr Johnson fuelled speculation about a future return to frontline politics despite promising his “most fervent support” to his successor Ms Truss.
Mr Johnson compared himself to Roman statesman Cincinnatus, who battled against invasion before returning to his farm. According to tradition, Cincinnatus later returned to serve a second term.
Some Tory MPs are reportedly openly suggesting that the party asks Mr Johnson to return to Downing Street, despite being ousted just three months ago.
Former culture secretary and ally of the former PM, Nadine Dorries, is one of those openly calling for Mr Johnson’s return.
“Only one MP has a mandate from party members and from the British public – a mandate with an 80 seat majority. Boris Johnson,” she said.
James Duddridge, a former parliamentary private secretary to Boris Johnson, added that it is time for his boss to “come back”.
Both The Daily Telegraph and The Times are reporting that Mr Johnson is expected to stand for the leadership.
Sky News understands that former home secretary Priti Patel will back Mr Johnson if he chooses to run.
The Liberal Democrats are calling for Mr Johnson to be blocked from standing as leader of the Conservative Party and prime minister.
Ms Braverman was the first to declare she was running to be the next Conservative Party leader in the summer, praised as a figurehead of the right of the party for her hard-line views on Brexit and for denouncing “woke nonsense”.
She threw her hat in the ring for the Tory leadership even before Boris Johnson had officially resigned.
“I love this country. My parents came here with absolutely nothing and it was Britain that gave them hope, security and opportunity and afforded me incredible opportunities in education and my career,” she told ITV at the time.
“I owe a debt of gratitude to this country and to serve as prime minister would be the greatest honour so yes I will try.”
After her shock resignation as home secretary on Wednesday for sharing secure information through a private email, Ms Braverman lashed out at Ms Truss’s “tumultuous” premiership and accused the government of “breaking key pledges” – including on immigration policy.
Ms Braverman, a former attorney general, only became home secretary on 6 September when Ms Truss brought her in to replace Priti Patel.
Her tenure was controversial, having accused Tory critics, who successfully forced Ms Truss into U-turning over plans to scrap the top rate of income tax, of a “coup”.
A source close to rising star Kemi Badenoch has suggested to Sky News that she is set to stand in the leadership contest.
“Now that the prime minister has announced her resignation, the party must unite around a new leader who restores trust in politics and delivers good government for the British people,” the source said.
“Kemi is in conversations with colleagues about how best to achieve this.”
Ms Badenoch stood in the Conservative leadership race over the summer, coming fourth behind Mr Sunak, Ms Mordaunt and Ms Truss.
Little known beyond Tory circles at the start of the race, the former equalities minister was a favourite among members to the right of the party.
Her summer campaign focused on cultural issues which she said had divided the party in recent years.
Sky News understands that the current justice secretary is taking soundings on whether to stand in the leadership election.
It is understood he could stand on a possible platform of being a pragmatist and a unifier.
Mr Lewis did not stand in the last leadership election, instead backing outgoing PM Liz Truss.
He has also served as Northern Ireland secretary.
Jeremy Hunt
The new chancellor was brought in to replace the sacked Kwasi Kwarteng.
Seen by many in his party as a safe pair of hands, Mr Hunt has twice unsuccessfully tried to become Tory leader and has previously served as foreign secretary, health secretary and culture secretary.
In the leadership race this year, he backed Rishi Sunak over Ms Truss after getting eliminated from the contest himself in the first round of voting.
He was in the final two contenders to be Tory leader in 2019 – but lost to Boris Johnson by 66% to 34% in the members’ vote.
Conservative MP Crispin Blunt has said Mr Hunt should be the party’s next leader.
“Jeremy Hunt has in a few short days impressively exercised his known personal qualities and has made the first critical contribution to restoring the primacy of serving the national interest. He should complete this work as our next prime minister,” he said.
But Mr Hunt has seemingly ruled himself out of a third run at the top job, telling Sky News’ political editor Beth Rigby: “I rule it out, Mrs Hunt rules it out, three Hunt children rule it out.”
And Sky News’ deputy political editor Sam Coates understands Mr Hunt will not be running to replace Ms Truss.