Four fire engines and around 25 firefighters were called to reports of a fire and explosion at a hotel on Peckham Road in Peckham.
A small part of a room on the first floor of the hotel, currently being used as a shelter for homeless people, was damaged by the explosion, which is believed to have involved a small cylinder.
Around 100 people left the building before the Brigade arrived. One man was taken to hospital by London Ambulance Service crews. Firefighters wearing breathing apparatus carried out a systematic search of the building to ensure there were no further casualties or people trapped.
The Brigade was called at 0144 and the incident was over for firefighters by 0521. Fire crews from Peckham, New Cross, Old Kent Road and Brixton fire stations were at the scene.
The cause of the incident is under investigation by the Brigade and the Metropolitan Police Service.