Up to half of the UK's shadow cabinet is set to resign in a bid to oust Labour leader Jeremy Corbyn, it is understood.
It comes after shadow foreign secretary Hilary Benn was sacked overnight after telling Mr Corbyn he had "lost confidence" in his leadership.
Hours later, shadow health secretary Heidi Alexander said she would resign.
Mr Corbyn faces a vote of no confidence over claims he was "lacklustre" during the EU referendum - but sources close to Mr Corbyn said he would stand again.
The sources said they were confident that Mr Corbyn would automatically be on the ballot paper in the event of a leadership contest - but different Labour sources disagreed about whether that would be the case.
Meanwhile, a shadow cabinet member told the BBC: "I imagine that there'll be a leadership election and Jeremy will win. But this is a total distraction."
On the sacking of Hilary Benn, a Labour source told the BBC Mr Corbyn had "lost confidence" in the shadow foreign secretary.
Newspaper reports suggested Mr Benn had been encouraging shadow ministers to resign if Mr Corbyn ignored a motion of no confidence.
Mr Benn said there was concern about Mr Corbyn's "leadership and his ability to win an election".
He said he had phoned the Labour leader to tell him "I had lost confidence in his ability to lead the party and he dismissed me".