Labour leadership: Liz Kendall endorsed by Chuka Umunna
Labour leadership candidate Liz Kendall has won the backing of shadow business secretary Chuka Umunna.
Mr Umunna, who pulled out the race himself earlier this month, said Ms Kendall was best placed to drag the party out of its "comfort zone".
He told the New Statesman Ms Kendall had "challenged conventional wisdom" and asked tough questions about Labour's future after its defeat.
Andy Burnham, Yvette Cooper and Mary Creagh are also standing.
Candidates must get the support of 35 MPs by 15 June, when nominations close, in order to get on the ballot paper. The winner will be announced on 12 September.
Ms Kendall was the first candidate to publicly declare her interest in the job after Ed Miliband's resignation.
The shadow care services minister, who was elected to Parliament in 2010, had already won the support of shadow education secretary Tristram Hunt and shadow Europe minister Pat McFadden.
Now Mr Umunna has said he is throwing his weight behind her and that three other MPs who were part of his short-lived leadership team - Emma Reynolds, Jonathan Reynolds and Stephen Twigg - were also doing the same.
"In this time of change our party must move beyond its comfort zone and find new ways of realising its age-old goals of equality and freedom," he wrote in the New Statesman.
Labour's next leader, he suggested, must embrace a "vision of a Britain in which all can get on, whose citizens are financially secure and in control of their lives and happiness - and are, collectively, secure and effective in the wider world".
"For us, our next leader must get this vision right," he wrote.
"On all these big subjects, Liz Kendall has asked the tough questions and started to chart a course to the answers. She has been courageous in challenging conventional wisdom. She has no compunction in moving Labour beyond our comfort zone and is determined to build a team ready to chart a route forward."
Ms Kendall has promised a new approach to business, education and defence, claiming Labour lost the election because its policies were wrong and mistakenly believed the county had moved to the left.
Mr Burnham has won the backing of frontbenchers Rachel Reeves, Dan Jarvis and Michael Dugher, as well as former deputy prime minister Lord Prescott. Yvette Cooper has been endorsed by Vernon Coaker and John Healey among others.
Ms Creagh told the BBC that she was confident that she would get sufficient nominations to get on the ballot paper. "A lot of people have already made a decision but a lot of people are rightly consulting with their parties," she told Radio 4's Woman's Hour.
While Labour could win the next election, Ms Creagh warned that the party would "cease to exist" if it took its voters for granted and did not address the separate challenges facing it in Scotland, the north of England and southern England.
Mr Umunna pulled out of the race only days after entering, saying he was uncomfortable with media scrutiny of his family.