Birmingham have sacked manager Gary Rowett after more than two years in charge of the Championship club.
Assistant boss Kevin Summerfield and coaches Kevin Poole, Darren Robinson and Mark Sale have also left the club.
In a statement on their website, the club said "an immediate replacement" would be found to give the new manager time to prepare for the upcoming January transfer window and funds would be available.
"Such a parting of the ways is always difficult, particularly so on a personal level as I have worked very closely with Gary and have got to know him well," club director Panos Pavlakis said.
"Our relationship was very strong but in football you can never stand still.
"I would ask that our supporters trust our judgment and look forward to and embrace the future as we begin to implement the exciting vision of [owners] Trillion Trophy Asia Limited."