Labour leader Jeremy Corbyn should resign for the good of the “party and the country”, Angela Eagle has said.
The ex-shadow business secretary, who is considering a challenge for the leadership, said the UK was in “crisis” and needed “strong opposition”.
It comes as former Labour leader Lord Kinnock said MPs were “fundamentally alarmed” by the party’s prospects.
But James Schneider, from grassroots movement Momentum, said Mr Corbyn still had “enormous support”.
Events have been taking place in support of the Labour leader, including in Leeds and Liverpool – where more than 1,000 demonstrators attended.
Mr Corbyn has come under increasing pressure from Labour MPs following the EU referendum, resulting in a host of shadow cabinet resignations.
On Tuesday, a motion of no confidence in the Labour leader was passed by the party’s MPs by 172-40 votes.
Ms Eagle and shadow secretary of state for work and pensions Owen Smith are both considering a challenge to Mr Corbyn.
Renewing her call for Mr Corbyn to resign, Ms Eagle said: “He’s lost the confidence of the parliamentary party.
“He’s losing confidence in the party. And let’s face it the country’s in a crisis and we need strong opposition.”
‘Clear, honest thing’
Earlier former Labour leader Lord Kinnock said he supported the moves to remove Mr Corbyn.
“I totally understand and I completely support the members of Parliament who voted in the no-confidence motion,” he told BBC Radio 5 Live,.
“They were doing the clear, honest thing when they are so fundamentally alarmed by the prospects for the party.”
BBC Newsnight understands shadow cabinet members are drawing up plans to encourage Mr Corbyn to resign.
A delegation of MPs tried to meet Mr Corbyn on Thursday to put forward their plan, but were unsuccessful, the BBC has learned.
Under the plan, potential leadership contenders would agree to pursue some of Mr Corbyn’s key policies on issues including tackling inequality and making the party more democratic.
Mr Corbyn has previously said he would not “betray” party members who elected him last year by standing down.
Momentum spokesman Mr Schneider told BBC Radio 4’s Today programme Mr Corbyn had shown “incredible steel” in remaining leader, and he accused other MPs of trying to “subvert democracy in the party”.
“If they are unhappy with Jeremy Corbyn’s leadership or the policies which he is standing for, they need to get 51 signatures, they need to find a candidate, they need to find a platform and they need to go for it,” he said.
“But they don’t have a candidate who can beat Jeremy Corbyn.”
He said there was a “reasonable amount of evidence” to suggest people who had joined the Labour Party in a recent surge had joined to support Mr Corbyn, as 60% of the first 13,000 members had put this on their joining form.
‘More serious than 1980s’
Meanwhile, former Welsh Secretary Lord Hain told the BBC’s Sunday Politics Wales programme he had never been as concerned as he was now about the party’s prospects ,saying it was “much more serious” than the “early 1980s strife”.
Mr Corbyn has faced a series of walkouts by shadow cabinet members and mounting calls for him to resign, following the EU referendum.
In the Commons last week Prime Minister David Cameron, told him: “For heaven’s sake man, go.”
Mr Corbyn’s predecessor, Ed Miliband, also told BBC Radio 4’s The World at One the Labour leader’s position was “untenable”.
But senior allies of Mr Corbyn, who has strong support among the party’s members, are determined to keep him in place.
Shadow Chancellor John McDonnell has said he is confident Mr Corbyn would see off any challenge to his leadership.