Boris Johnson has taken a commanding lead in the race to become Britain’s next prime minister, winning the lion’s share of support in first-round voting by Conservative Party politicians.

Mr Johnson, who has pledged to deliver Brexit on October 31, surged closer to power on Thursday (British time), with 114 of 313 votes in his favour.

The result reduced the field of candidates to replace British Prime Minister Theresa May from 10 to seven.

Mr Johnson, a former foreign secretary and leading Brexit campaigner who formally launched his campaign for the top job only a day before, was trailed by his successor as foreign secretary, Jeremy Hunt (43 votes) and Environment Secretary Michael Gove (37).

“Thank you to my friends and colleagues in the Conservative & Unionist Party for your support. I am delighted to win the first ballot, but we have a long way to go,” he tweeted afterwards.

The result exceeded the expectations of Mr Johnson’s team. It means he is almost certain to be among the final two candidates who will be put to a vote of 160,000 party members nationwide. The winner will become Conservative leader and British PM.

Dame Cheryl Gillan reads out the results of the first ballot in the leadership contest. Photo: AAP

Three candidates were eliminated in Thursday’s vote. MPs Esther McVey, Mark Harper and Andrea Leadsom all failed to reach the threshold of 17 votes needed to get to the next round.

“Boris did well today but what the result shows is, when it comes to the members’ stage, I’m the man to take him on,” Mr Hunt told the BBC.

The contest is dominated by the issue of Britain’s stalled departure from the European Union, with all the contenders promising to succeed where Ms May failed and lead the country out of the bloc.

Ms May quit as party leader last week after failing to secure Parliament’s backing for her Brexit divorce deal. Britain’s EU departure was originally set for March 29, but has been delayed to October 31 because of the political deadlock in London.

Mr Johnson vowed on Wednesday that as prime minister he would “get Brexit done”, either by renegotiating Ms May’s rejected Brexit deal or by leaving the EU on October 31 without an agreement.

“Delay means defeat” for the Conservatives, he said.

Mr Johnson has spent weeks wooing Conservative MPs, although staying out of the spotlight with a low-key campaign at that is at odds with his flamboyant publicity stunts of the past.

Despite his long record of scandals and gaffes, he has been given a 70 per cent chance of winning the job by betting markets.

Conservative MPs will hold further elimination rounds of votes next week until two contenders remain. They will be put to a postal ballot of party members, with the winner due to be announced the week of July 22.

The other four contenders in remaining in the race are ex-Brexit Secretary Dominic Raab, Home Secretary Sajid Javid, Health Secretary Matt Hancock and International Development Secretary Rory Stewart.

-with AAP