Slaven Bilic has been sacked as West Ham manager.
The Premier League club announced the departure of the Croatian, who was appointed in June 2015 on a three-year contract, on Monday after Saturday's 4-1 loss to Liverpool.
"West Ham United can confirm that Slaven Bilic has today left his position with the club," the Hammers said in a statement.
The club hierarchy "believe a change is now necessary in order for the club to move forward positively and in line with their ambition", the statement added.
Former Everton, Manchester United and Sunderland boss David Moyes is widely expected to replace Bilic at the London Stadium.
The Hammers statement added: "The club's search for a new manager to take West Ham United forward is underway and an announcement regarding Bilic's successor is expected to be made over the coming days."
Bilic's assistants Nikola Jurcevic, Edin Terzic, Julian Dicks and Miljenko Rak have also left the club with immediate effect.
West Ham are 18th in the Premier League with nine points from 11 games which have featured two wins - over Huddersfield and Swansea in September - three draws and six losses.
The manner of the latest capitulation at the London Stadium, coming just a fortnight after an equally desperate 3-0 home loss to newly promoted Brighton, saw co-chairmen David Sullivan and David Gold, plus Karren Brady, the vice-chairman act.
Moyes has already expressed his interest in succeeding Bilic.
"I'm interested, yes," he told beINSPORTS.
"I've had no contact from West Ham but I've always said I want to go back into club management. If the right opportunity comes around, I'd be interested."
The Scot did show some empathy with Bilic, despite effectively touting for his office.
"For me to get back in it means another manager is going to have to lose their job and I wouldn't wish that on anybody," he said.
"He (Bilic) must be hating it and wanting to get a result as soon as he can. So if it becomes available, yes, but at the moment it's not available."
Asked if he might be managing again after the forthcoming international break, he added: "I really don't know. I hope so."
Gold and Sullivan said the decision to axe Bilic had been made with "heavy hearts".
The duo praised Bilic for his role in the move from Upton Park to the former Olympic Stadium, particularly the concluding win over Manchester United in the final home game of 2015-16 which helped to earn a seventh-place finish in his first season as boss.
But recent results "have not been of the expected standard" and the Hammers hope a change in management can see the team climb into the top half of the table.
Gold and Sullivan added in a statement posted on whufc.com: "During the summer, the board invested heavily signing the players Slaven believed would complete the squad he needed to push the club back towards the level we had reached in his first season, and we believe we have the players capable of doing that.
"We have not seen enough indication of the required improvement to give us the encouragement that things would change and we would meet our Premier League aspirations this season.
"We believe a change is now necessary to ensure we can begin to move the team back in the right direction.
"We see this as an exciting opportunity to appoint a quality manager to the position to inject fresh ideas, organisation and enthusiasm into a very talented squad."