A great white shark has been sighted circling a whale carcass near a popular Perth beach.

Floating about six nautical miles west of Scarborough Beach, the carcass is believed to have attracted the shark, which was spotted on Sunday.

WA Department of Fisheries spokesman Tony Cappelluti said he was concerned the dead whale would float closer to the shoreline.

"While the carcass is a long way off any Perth beaches, it is important that boat users or divers are aware of the potential increased shark activity near the carcass," Mr Cappelluti said.

"There has also been another shark sighting (Sunday) morning at Strickland Bay on Rottnest Island, where warning signs were erected several days ago after sightings made during the week."