LONDON (AFP) - Theresa May emerged on top after the first round of voting for Britain's next leader as MPs cast their initial ballots in the contest to replace David Cameron on Tuesday.

The home secretary received 165 votes from her fellow Conservative lawmakers, followed by previously untipped junior energy minister Andrea Leadsom in second place on 66 votes.

Right-winger Liam Fox became the first candidate to be eliminated from the race after coming last in the contest with 16 votes.

Conservative lawmakers are scheduled to hold further ballots on Thursday and next Tuesday, eliminating the least popular candidate each time, for as long as it takes to whittle down the race to two contenders.

This pair will then be put to a vote of around 150,000 Conservative party members throughout the country.

The final result will be announced on Sept 9.

Whoever wins will become both the next leader of the ruling Conservative party and the prime minister, after Cameron announced hours after the results emerged of last month's referendum vote to leave the European Union.

The prime minister himself did not take part in the vote to choose his successor and is not expected to express a preference for any of the candidates.

May was in favour of remaining in the EU during the referendum, while Leadsom campaigned to leave.

Pro-Brexit Justice Secretary Michael Gove - who has lost popularity among MPs after effectively ending former London mayor Boris Johnson's leadership run - came in third in Tuesday's vote with 48 votes.

Work and Pensions Secretary Stephen Crabb was fourth with 34 votes. He later pulled out of the race and endorsed front-runner May.

The results of Tuesday's vote were announced in the House of Commons by senior Conservative MP Graham Brady, chairman of the 1922 Committee of Conservative MPs which is running the contest.