ITV has said the Good Morning Britain studios were evacuated yesterday "as a precaution".
"It was an isolated incident which was quickly resolved," the broadcaster said in a statement.
Viewers at home were left watching a pre-recorded interview when the fire alarm went off mid-broadcast.
Presenters Ben Shephard and Susanna Reid were interviewing Emmerdale actors Charley Webb and Anthony Quinlan via a live link from Yorkshire when the alarm at the London Television Centre went off.
Reid said: "Terribly sorry."
A member of staff who did not want to be named said a "fuse box overheated and went on fire on the third floor" where Good Morning Britain is filmed.