Firefighters are warning people to be extra vigilant about dropping cigarette butts and glass bottles after two grass fires in a park.

Wimbledon fire officers were called to a fire in Wandle Meadow Nature Park, off North Road at about 8pm last night.

A fire officer who was on duty said about half a hectare of land behind Garfield Primary School was smoking.

"If you have a bottle or a cigarette, don't just throw it - especially at this time of year", he said.

The fire was believed to have been caused by a glass bottle magnifying the rays of sun which ignited the vegetation.

It was extinguished in about half an hour.

The grass fire was the second in the park this week - after temperatures soared above 30 degrees Celsius.