Former finance minister Rishi Sunak led the field of Conservative MPs bidding to become Britain's next prime minister in the first ballot of Tory lawmakers on Wednesday, as the race narrowed to six with the elimination of two candidates.

Early frontrunner Sunak – who quit as finance minister last week, helping to trigger outgoing Prime Minister Boris Johnson's downfall – topped the contest with 88 votes, followed by former defence minister Penny Mordaunt, on 67.

Foreign Secretary Liz Truss finished third, winning the support of 50 of the 357 Conservative lawmakers who voted.

The remaining candidates to meet Wednesday's minimum 30-vote threshold were former equalities minister Kemi Badenoch, on 40, backbencher Tom Tugendhat, on 37, and Attorney General Suella Braverman, who scraped through with 32 votes.

However, former foreign secretary Jeremy Hunt, who finished runner-up to Johnson in the last contest in 2019, and newly appointed finance minister Nadhim Zahawi were eliminated after struggling to hit the target.

There will be no let-up to the contest, with another round of voting set for Thursday, as the ruling party tries to winnow the candidates list down to a pair over the next week to then put to party members.

Several television debates between the remaining candidates loom, with the first on Friday night, ahead of weeks of nationwide hustings during the final run-off race.

The eventual winner is set to be announced on September 5, as the party seeks to rebuild its support following near non-stop scandal under Johnson ahead of the next general election due in 2024.

But the battle has already been marked by infighting between the candidates, prompting the beaten Hunt to warn the remaining rivals that "smears (and) attacks may bring short-term tactical gain but always backfire long term". (AFP)