Britain's opposition Labour will name its new leader on September 12 after Ed Miliband resigned in the wake of last week's bruising election defeat, the party's executive committee said Wednesday.
Nominations to replace Miliband will close on June 15, the centre-left party said.
Liz Kendall, Labour's spokeswoman for care and the elderly, and Chuka Umunna, spokesman on business, had earlier declared they would run for the party leadership.
Health spokesman Andy Burnham and former work and pensions minister Yvette Cooper joined them by announcing their candidacies on Wednesday.
Education spokesman Tristram Hunt is also seen as a potential contender.
Bookmakers' favourite Umunna, 36, would be the first leader of a major British political party from an ethnic minority but is seen by critics as too inexperienced, having been elected to parliament only in 2010.
Divisions have emerged within the party over whether its general election campaign was too left-wing -- or not left-wing enough.
Former prime minister Tony Blair and supporters of his centrist "New Labour" approach were particularly critical of Miliband's pitch.
In announcing his candidacy, Burnham said: "Our challenge is not to go left or right, to focus on one part of the country above another, but to rediscover the beating heart of Labour."
Cooper vowed to improve life for families, while saying it would be wrong to "go back to the remedies of the past" that helped Blair win three elections.
Prime Minister David Cameron's Conservatives won the May 7 election with 331 out of the 650 seats in the House of Commons, against 232 for Labour.
"The general election saw the Labour Party suffer a serious defeat and over the coming weeks we need an open and honest debate on the right way forward," said interim party leader Harriet Harman.
Leadership contenders need the support of 15 percent of Labour lawmakers, which works out at 34.
Party members, registered supporters and affiliated supporters get one vote each.
The new leader will be in place for the party's annual conference on September 27.
Meanwhile, the media appeared to be closing in on the much-mocked "EdStone", a 2.6-metre-high monument with vague-sounding Labour election pledges carved in stone.
Unveiled by Miliband in a car park on May 3, the monolith was destined for the garden of 10 Downing Street if Labour won -- but mysteriously vanished without trace when it didn't.
The Guardian newspaper said it understood the policy tablet was "languishing in a south London garage" where it is "kept under lock and key, to avoid any discovery which might cause further embarrassment".