A bin was set alight in a shed outside a block of flats in Sutton on Sunday night.
Firefighters were called to Brendon House in Sutton Court, off Brighton Road, just after 8pm on Sunday after a fire was discovered in a bin store attached to the main building via a chute.
A witness said: "Orange flames were clearly visible through the ventilation area above the wooden doors. Later smoke started pouring out of the ventilation.
"When a firefighter opened the wooden doors large flames came pouring out."
A crew from Sutton fire station used a hose to douse the flames and then damped down the roof of the shed.
A fire service spokesman said the fire looked as if it had been started deliberately and police are investigating.
If you have any information you can call police on 101 or the charity Crimestoppers on 0800 555 111.
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