Manager David Moyes has left West Ham after just over six months in charge despite guiding the club to Premier League survival.
Moyes, 55, took over from Slaven Bilic on a short-term contract in November with the club in the relegation zone.
West Ham secured safety with two games to spare and finished 13th. Moyes met senior figures at the club on Monday.
The former Everton and Manchester United boss recorded nine wins and 10 draws from 31 games as West Ham boss.
"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," said West Ham joint-chairman David Sullivan.
"We feel that it is right to move in a different direction. 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."
Moyes' assistants Alan Irvine, Stuart Pearce and Billy McKinlay have also left with immediate effect.
'Even Guardiola took a bit of time to get his team right'
West Ham finished nine points clear of the drop zone, after earning seven points out of the last nine.
Moyes' last game in charge was a 3-1 win over Everton on Sunday, after which he suggested his preference was to stay beyond this season.
"Everybody always thinks the grass is greener and there's something better out there. I would say more often than not I bet you it's proved wrong," said Moyes.
"We've shown we're trying to improve. I don't know if anybody can come and make that big a difference in six months. Even Pep Guardiola took a bit of time to get his team right.
"I'd think you'd need to give a bit longer. But every manager now is in transit. I don't think there is a long period."
The right man to turn things around?
Moyes had been out of work since May 2017, when he resigned as Sunderland manager after the club's relegation to the Championship.
West Ham joint chairman David Sullivan said the Scot was "the right man to turn things around".
Moyes lost his first game in charge as West Ham were beaten 2-0 at Watford on 19 November and they picked up just one point from his first four Premier League matches as manager.
They beat Chelsea 1-0 on 9 December for his first win and the Hammers began 2018 one point above the relegation zone.
However, four games without a win, including an FA Cup exit at League One Wigan, increased the pressure on Moyes.
Supporters invaded the pitch during the 3-0 home defeat by Burnley on 10 March which was West Ham's third consecutive league defeat. That left them 16th in the table, three points above the relegation zone.
The Hammers beat relegation rivals Southampton 3-0 at London Stadium in their next game, while back-to-back draws against Chelsea and Stoke further steadied the ship.
Following defeats by Arsenal and Manchester City, West Ham ended the season with a 2-0 win at Leicester, goalless draw with Manchester United and the victory over Everton.
BBC Sport's Frank Keogh
David Moyes achieved what he was brought in to do - save West Ham from relegation - but he had never really looked like being the long-term manager, despite positive comments from Hammers co-owner David Gold.
Moyes may well feel his stint should lead to another Premier League job, while Gold and David Sullivan are faced with one of the most crucial appointments in the club's history.
It comes against a backdrop of fan protests and antagonism among a significant section of supporters who are unhappy at the move from Upton Park to the London Stadium and also want greater investment in the side.
The Hammers hierarchy have been long-term admirers of Rafael Benitez, but he may choose to stay on at Newcastle, while former Manchester City boss Manuel Pellegrini and outgoing Paris St-Germain coach Unai Emery have been linked with the role. Sullivan has also reportedly held talks with Shakhtar Donetsk manager Paulo Fonseca.