David Moyes has left West Ham following the end of his short-term contract.
Moyes' assistants Alan Irvine, Stuart Pearce and Billy McKinlay have also departed with immediate effect.
The announcement arrived barely 12 hours after David Gold, West Ham's co-owner, said he hoped 55-year-old former Manchester United and Everton boss Moyes would remain in charge for next season.
Joint-Chairman David Sullivan said: "I would like to place on record my sincere thanks to David Moyes and his staff for achieving the target of keeping West Ham United in the Premier League.
"Throughout his time here, David has carried himself with dignity and honesty and we have all found him to be a pleasure to work with.
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Moyes guided West Ham to a 13th-place finish
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"He, Alan, Stuart and Billy accepted the challenge and attacked it head on, turning around a difficult situation. They deserve great respect for the job they have done and they leave the club with our best wishes.
"When David and his team arrived, it was the wish of both parties that the focus be only on the six months until the end of the season, at which point a decision would be made with regards to the future.
"Having taken stock of the situation and reflected now the campaign is complete, we feel that it is right to move in a different direction.
"We are already taking steps to identify and recruit the manager we believe can take West Ham United forward in line with our ambitions.
"We aim to appoint a high-calibre figure who we feel will lead the club into an exciting future for our loyal supporters within the next 10 days."
Sky Sports News understands that Newcastle boss Rafael Benitez and former Manchester City manager Manuel Pellegrini are on the shortlist to replace Moyes.
It is also understood that between 30 and 40 managers have expressed an interest in the job.
Moyes was appointed as Slaven Bilic's successor in November last year with the club in the relegation zone.
The Hammers finished in 13th place in the Premier League but their season has been marred by fan unrest, culminating in a pitch invasion during their 3-0 defeat to Burnley in March.