BBC Radio 2's breakfast DJ Sir Terry Wogan was forced off air after steam from a nearby gym activated the fire alarms in his studio.
Sir Terry joined BBC staff outside Western House during the alert
An emergency tape of non-stop music played as staff evacuated the BBC's Western House complex, next to Broadcasting House in central London.
Digital station 6 Music's breakfast show, with Phill Jupitus, was also taken off air for 10 minutes.
A BBC spokeswoman said the steam came from a staff gym in the building.