The Jermyn Street Theatre was flooded yesterday.
A flood five feet in depth ruined the venue's workshop, technical store, props and furniture store, dressing rooms, offices and archives, after a pipe burst in an adjacent building.
The theatre's artistic director Tom Littler, said: "There were thankfully no injuries yesterday, and we offer huge thanks to the teams from the London Fire Brigade and Thames Water. We are now assessing the extent of the damage and our insurance cover.
"Anyone who knows our co-founders Penny Horner and Howard Jameson will know what a huge blow this is to them personally as well as to our theatre. Penny was, as always, a true theatre hero, working through the night without sleep. Please keep her and our theatre in your thoughts this Easter weekend."
The venue is asking for donations as it continues to remain closed throughout the coronavirus outbreak.