Theresa May has formally resigned as Conservative Party leader to allow the official start of the contest to replace her.
Officials from the Tories’ 1922 Committee confirmed in a statement that the prime minister had quit as leader.
However, she will stay on as acting leader until her successor has been elected.
The 1922 Committee said it was now inviting nominations from Conservative MPs who wish to take over from Mrs May. They have until 5pm on Monday to formally apply.
So far, 11 candidates have publicly declared their intention to enter the contest.
They will face rounds of voting among MPs to choose a final pairing, with the winning candidate then chosen by a postal ballot of Conservative Party members.
It is expected the Tories’ grassroots will be asked to submit their votes by 5pm on 22 July, meaning a new Conservative leader – and therefore prime minister – will be in place as early as 23 July.
Downing Street has been keen to make Mrs May’s formal resignation as Tory leader a low-key event, with the prime minister likely to stay in office for many more weeks.
Sources suggested it was important that Mrs May remains PM in the public’s mind.
According to reports on Friday, Mrs May is at odds with Chancellor Philip Hammond over plans for a series of spending announcements during her remaining time in office.
The Financial Times said the Treasury estimated Mrs May’s proposed promises – including a boost to education funding – could cost more than £10bn and might eat into Mr Hammond’s “war chest” for a possible no-deal Brexit.
Ahead of her last few weeks, Mrs May’s spokesman said on Thursday: “You heard the prime minister talk passionately about some of the domestic policy issues which she cares about.
“She will continue to focus on trying to deliver for the people of this country.”
Mrs May entered Downing Street in 2016 with a pledge to tackle the “burning injustices” in society.
But she has seen much of her time dominated by the Brexit deadlock, which eventually led her to tearfully announce her intention to resign outside Number 10 last month.
Mrs May’s last appearance on the world stage as prime minister could be the G20 summit in Japan on 28-29 June.
Those vying to replace her include five members of her cabinet; Home Secretary Sajid Javid, Health Secretary Matt Hancock, Foreign Secretary Jeremy Hunt, International Development Secretary Rory Stewart and Environment Secretary Michael Gove.
Her former ministers Boris Johnson, Dominic Raab, Andrea Leadsom, Esther McVey, and Sam Gyimah have also entered the race, along with David Cameron’s former chief whip Mark Harper.