Police say six fires were lit deliberately across several Perth suburbs within a two hour period yesterday.
The fires in Whiteman Park, Middle Swan, Malaga and Eden Hill were all extinguished.
Police are investigating and appealing for information from the public.
The Department of Fire and Emergency Services says arson attacks in the South West have come close to claiming lives.
More than 25 fires have been deliberately lit in Busselton in the last month, causing widespread damage.
A fire just south of the town burned for hours yesterday, as more than 80 firefighters battled strong winds to try to bring it under control.
The department's Danny Mosconi says the blaze could have had serious repercussions.
"Unfortunately, it was very close to destroying one property, and if it wasn't for the great work of the firefighters, this house could have also been damaged, lost or even worse, someone could have been injured or lost their life," he said.
Authorities say a preliminary investigation has found a bushfire which threatened lives and homes near the South West town of Harvey last week was caused accidently by a contract worker.
An emergency warning was advised as the fire burnt north of Benger Swamp Nature Reserve, about 10 kilometres south west of Harvey.
The Department of Environment and Conservation says preliminary investigations found a contractor spraying weeds caused the blaze through the exhaust of his quad bike.
"The exhaust from the quad bike, there's been some sort of an issue with that, and it has ignited a few spots of fire," he said.
The department's Peter Dans says the fire burnt about 300 hectares.
"It was pretty well contained by about 9:00 or 10:00 pm on that actual Monday evening,"
"It is a concern and we'll have to review procedures for our contractors just to ensure that something like this isn't repeated again."