A whale remains stranded on a sandbar off Rockingham Beach.
The 15-metre sperm whale was reported by a member of the public off Naval Memorial Reserve around 5.02am on Monday.
The whale is believed to be the same one that came close to swimmers at Port Beach near North Fremantle on Saturday.
Department of Biodiversity Conservation and Attractions (DBCA) officers have observed the whale from a boat and say it is "alive" and "breathing slowly".
Authorities anticipate it will be a "multi-day response for operational staff".
For safety reasons, members of the public are being urged to stay away from the beach.
It will remain closed until further notice.
A shark advice has also been issued as the whale could attract sharks to the area.
If you see a shark, report it to Water Police on 9442 8600.