Four fire engines and around 25 firefighters were called to a fire at a hotel on Dunheved Road South in Croydon.
An electrical plant room in the basement of a four-storey hotel was alight. Around 150 people were evacuated by hotel staff before the Brigade arrived. There were no reports of any injuries.
The Brigade was called at 0820 and the fire was under control by 0908. Fire crews from Norbury, Croydon and Tooting fire stations attended the scene.
The fire is believed to have been accidental and caused by resistive heating in a timer switch used as part of the hot water system.