Conservative MPs have voted in the first ballot of the Tory leadership contest – in which at least one contender will be knocked out.
Leadership hopefuls need at least 17 votes in the secret ballot to go through to the second round, with anyone below that threshold automatically eliminated.
But even if all the candidates meet the target, the one with the fewest votes overall will still have to exit the race.
The result is expected to be announced at 1pm.
Brexiteer Jacob Rees-Mogg, who is backing front-runner Boris Johnson for the top job, warned that more than one candidate could be knocked out.
He told the Press Association: “Mark Harper doesn’t seem in a very strong position.
“The bottom one goes and anyone under 5% goes. So, it could be more than one who’s knocked out.”
Andrea Leadsom, who is among the 10 candidates, said she was feeling “very positive and optimistic and hopeful that I will be getting enough support from colleagues to go through to the next round”.
Environment Secretary Michael Gove said he had voted for the “best candidate”.
And former work and pensions secretary Esther McVey told the Press Association: “I’m the outsider, I know that.”
Asked who she would urge her supporters to back if she is eliminated, she said: “I’m not answering that yet.”
Other candidates in the race include International Development Secretary Rory Stewart, Foreign Secretary Jeremy Hunt, Health Secretary Matt Hancock, Home Secretary Sajid Javid and former Brexit secretary Dominic Raab.
Earlier, Tory former minister Sir Oliver Letwin warned that Parliament may have run out of options to block a no-deal Brexit by the next prime minister.
The Commons voted on Wednesday to reject a Labour motion, backed by other opposition parties, which would have enabled MPs to take control of the business of the House with a view to preventing a no-deal.
Sir Oliver, who was behind a series of cross-party attempts to block a no-deal, said there may be no more opportunities for Parliament to intervene.
“Under the Article 50 process, on October 31 the UK leaves the EU regardless of whether we do or don’t have a deal in place unless somebody does something to alter that,” he told BBC Radio 4’s Today programme.
“If the Government doesn’t bring something before Parliament, Parliament won’t have a chance to take a view on that as things currently stand because we have run out of all the possibilities any of us can, at the moment anyway, think of for Parliament to be able to insist on having a view.
“I have really struggled very hard to think of every available opportunity and I can’t currently think of any more.”