A smoke alarm helped a man escape a fire on the lower ground floor of a block of flats on South Lambeth Road.
The fire is believed to have started in the electrical room in the communal corridor.
London Fire Brigade spokesperson said:
"Once again smoke alarms show how vital they if there is a fire in your property. After being alerted the man did exactly the right thing which was to get out, stay out and call 999. He also waited outside the building so firefighters knew where to go.
"Everyone should have at least one smoke alarm on every level of your home and the safest option is have those linked together. This will give the earliest warning if there is a fire in your home."
Ten firefighters and two fire engines from Lambeth Fire Station attended the incident. The Brigade was called at 2150 and the fire was under control by 2202. The cause of the fire is being treated as accidental.