Wes Streeting, who resigned as U.K. health secretary this week, announced Saturday he will run to replace Keir Starmer as Labour leader and prime minister, after the party suffered disastrous local election results.

"We need a proper contest with the best candidates on the field, and I'll be standing," Streeting said at a think tank event in London, two days after Greater Manchester mayor Andy Burnham unveiled a bid to become a member of Parliament, or MP.

If successful, that would allow Burnham to run in a Labour leadership contest that now appears all but inevitable, though it is yet to be formally triggered by MPs.

Streeting wrote in a scathing resignation letter challenging Starmer's leadership that he does not see the prime minister as being able to "lead the Labour Party into the next general election," and noted that where the party needs "vision," there is a "vacuum."

His letter followed the resignations of four other members of Starmer's government after the losses in the local elections. Nigel Farage and his right-wing populist party Reform U.K. made significant gains across England in those elections. 

Streeting, whose political ambitions have long been known, is one of several challengers who could try to unseat the prime minister. 

Challengers must get support from at least 20% of the Labour Party's members of parliament to trigger a leadership election, according to the party's rules.

Starmer has vowed to remain in office, warning lawmakers that any leadership contest would plunge the government into "chaos" at a time it should be focused on issues like the cost of living crisis and war in the Middle East.

He has been in office for just under two years after Labour won a landslide in the last national parliamentary elections.