350-hectare Sydney bushfire 'suspicious'

A fire that destroyed 350 hectares of national parkland south of Sydney at the weekend appears to have been deliberately lit.

Police are appealing for information about the blaze, which was sparked by a grass fire in the Kamay Botany Bay National Park on Sunday afternoon, as arson investigators scrutinise the "suspicious" fire.

Up to 100 rural firefighters battled dangerous conditions to bring it under control.

"Police have issued a strong warning to potential bushfire arsonists that it is not just the eyes of emergency services, but the wider community, that will be watching for any suspicious activity which leads to bushfires," Superintendent Murray Chapman said in a statement.

"Lighting bushfires isn't just illegal and dangerous, it can be deadly ... You could face penalties of up to 25 years' imprisonment."