Firefighters were called to Southwark Bridge Road on at 5.30pm on Wednesday night to tackle a blaze at the London Fire Brigade's own training centre.
The brigade sent four fire engines to the £22 million centre in Southwark after receiving an emergency call.
"A small fire has occurred in one of the buildings at the London Fire Brigade training centre in Southwark" said a brigade spokesman.
"The building is designed for firefighter training purposes, but was not being used when the fire started. As with any incident the cause of the fire is being investigated."
Firefighters said the seat of the blaze appeared to be in insulation materials inside a wall in the Fire House – a replica of a home fitted with gas and electrical appliances for training purposes.
According to the Evening Standard the alarm was only raised after an off-duty fireman dialled 999.
Crews reportedly worked through the night to ensure the fire did not spread.