Labour MPs have backed a motion of no confidence in party leader Jeremy Corbyn by 172 to 40.
The vote is non-binding.
Earlier, one of the party leader's closest allies warned vote of no confidence in Jeremy Corbyn by Labour MPs would have "no meaning".
Diane Abbott, the newly appointed shadow health secretary, said MPs would have to mount a full leadership challenge if they want to get rid of Mr Corbyn.
And she said the outcome of any contest would still be decided by the grassroots activists who swept Mr Corbyn to the leadership in last year's election.
Her warning came before MPs voted on a no confidence motion tabled by veteran backbencher Dame Margaret Hodge in a secret ballot.
Mr Corbyn's leadership has been rocked by the mass resignations of dozens of frontbench shadow ministers including more than half the shadow cabinet.
Rebels are hoping that a vote of no confidence by the Parliamentary Labour Party would force him to quit.
However, Ms Abbott said the vote had no status under the party rule book.
"It has no meaning," she told BBC Radio 4's Today programme. MPs don't choose the leader of the Labour Party, the party does.
"I think it is really sad that colleagues have chosen to stage this three-ring circus because they don't want to have a leadership election because they are not certain of winning a leadership election.
"The way to resolve this is to have a leadership election."
Furious Labour MPs told the leader to his face that he must quit for the good of the party at a heated meeting in parliament on Monday night.
But a defiant Mr Corbyn is refusing to bow to "a corridor coup" despite losing around 40 members of his frontbench team in just two days.
Significant numbers of supporters turned out to show solidarity for the embattled leader at a rally in Parliament Square.
Mr Corbyn appealed for "unity" and told the crowd: "Don't let the people who wish us ill divide us."
But at a brutal meeting of the Parliamentary Labour Party the Opposition leader was told he was not up to the job and was urged to "do the decent thing".
The Labour-supporting Daily Mirror joined the calls for him to quit for the sake of his party and country.
Shadow justice minister Andy Slaughter became the latest to quit - after declining the offer of a role in the shadow cabinet.
"With much regret I have resigned from the Labour frontbench after six years as a shadow minister," he said.