Alan Pardew has been sacked as West Ham manager after a string of defeats.
The decision was taken this morning by Hammers new chairman Eggert Magnusson and the club will seek to appoint a successor before the January transfer window.
West Ham said in a statement: 'West Ham United have today announced the departure from the club of Alan Pardew.
'Alan has made an important contribution since joining as manager in September 2003 but this season's results have been disappointing and have left the club in a very difficult position.
'The chairman, Mr Eggert Magnusson, and the board have been concerned by the performances of recent weeks and feel that it is the right time to make a change in the best interests of the club.
'Mr Magnusson and the board would like to place on the record their thanks to Alan Pardew for his hard work and commitment and to wish him well for the future.
'The search for a successor is now under way in order that a new manager can be in place ahead of the January transfer window.
'First-team coach Kevin Keen will take temporary charge of team affairs until a new appointment has been made. No further statements on this matter will be made by the club before that time.'
The Hammers have lost five out of their last six Premiership matches including both games since Magnusson became chairman - a 4-0 at Bolton on Saturday which followed a 2-0 home defeat against Wigan.
Magnusson had promised to keep faith with Pardew, and the pair had held meetings about possible targets for the January transfer window, but the club's slide into the bottom three caused alarm bells to ring.
The chairman and Icelandic banking mogul Bjorgolfur Gudmundsson, who provided most of the cash for the £85million takeover, were both present at the defeat by Bolton.
The new owners have made contingency plans in the event of relegation but the consortium's business plan was very much targeted to West Ham remaining in the top flight and taking advantage of the bumper new Premier League TV rights deal which comes on stream next season.
West Ham's first game without Pardew could not be much tougher - a home match against league leaders Manchester United on Sunday.
Their Christmas fixture list of matches feature games against Fulham, Portsmouth, Manchester City and Reading.
Possible successors include Alan Curbishley, who has a proven track record in the Premiership and Sven-Goran Eriksson, who has still yet to find a job since stepping down as England head coach.
Pardew said he left the club feeling proud of his achievements.
'When I took the helm they were in the Championship and struggling to find direction,' he told the club's website.
'In two consecutive seasons we qualified for the play-offs, ultimately achieving the Premiership status the club so richly deserve.
'I am also proud of our first season back in the top flight in which we finished ninth and came so close to winning the FA Cup.
'The supporters have stood by me and I will always cherish memories of their support and loyalty during the difficulties of this season.
'I am proud most of all of the players, many of whom have developed into top Premiership performers under the tutelage of myself and my backroom staff.
'The coaching and medical staff at Upton Park are second to none and I want to wish the new chairman Eggert Magnusson and the club every success for the future.'
Alan Curbishley's agent Phil Smith has played down bookmakers' moves to install his client as favourite to take over from Pardew.
'I keep in touch with Alan every day. I have not heard anything at this point at all,' Smith said.
'But I can't say what will happen in the next 24, 48 or 72 hours.
'There has been no discussion with West Ham and if or when there is an approach we will deal with it.'