Breaking: Suspected shark attack at Sorrento beach in Perth's north - ABC News & Headlines – Australian Broadcasting Corporation

Water Police are on the scene of the suspected shark attack at Sorrento. (ABC News )

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 currently patrolling the beach, and officers could be seen standing along on the shoreline next to a red surfboard. 

 A police helicopter was also seen hovering overhead in the same spot.

An aerial and water search is underway at Sorrento Beach.  (ABC News )

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

A witness has described her shock after seeing blood in the water.

Jacqui said she had been at a nearby cafe when her friend drew her attention to the beach.

""My friend said, "Jack, I think there's been a shark attack" and I looked out to the ocean and I could see a pool of blood," she told the ABC. 

She said she believed two men had been swimming but only one of them had made it back to shore.

Ms Rapaic said those on the shore were shocked by the scenes and felt helpless watching.

Russell James was also there when the shark alarm sounded.

Crowds have gathered on the path above the beach. (ABC News )

"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.

Police are patrolling Sorrento Beach following a suspected shark attack.  (ABC News: Andrew O'Connor )

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