Shark attack at Sorrento beach in Perth's north

Emergency services are responding to reports of a suspected shark attack at Sorrento beach north of Perth.

St John WA received reports of the suspected attack at 10:15am local time and have confirmed three crews have been sent to the scene, including one on priority. 

WA police are also at the scene.

The beach has been closed to swimmers and people are being advised to take caution.

Russell James was at the beach when the shark alarm sounded.

"The helicopter was circling around and then the police boat came in," he told the ABC.

"There were a bunch of police and ambulances and a few people standing down by the water's edge near the groyne … there appeared to be a couple of surfboards or paddle boards down by the beach."

The suspected attack comes just a week after Surf Lifesaving WA's helicopter shark patrols began for the summer season.

Earlier, a member of the public reported seeing a 2.5 metre-long shark off the beach.

Sorrento is a popular swimming spot, located about 20 kilometres north of the CBD and just south of Hillarys marina which boasts several restaurants and cafes.