A swimmer has been killed in a shark attack at a beach in Perth’s northern suburbs.

Police confirmed the male swimmer died as a result of the attack, but provided no further details.

Earlier, a witness described seeing blood in the water after a shark attack at Sorrento Beach.

This is the second shark attack in WA so far this week, and has triggered the closure of almost 12 kilometres of beach from Marmion to Iluka until at least noon on Saturday.

St John WA had received reports of the attack at 10:15am local time.

A water police speedboat travels in open ocean near the shore, while a helicopter flies above.

Police are at the site of the suspected shark attack off Sorrento Beach. (ABC News: Andrew O’Connor)

WA police have been patrolling the beach since, with officers earlier seen standing along the shoreline next to a red surfboard.

Witness saw blood

Witness Jacqui Rapaic described her shock after seeing blood in the water.

Police standing on a beach

Police are patrolling the beach, which is now closed. (ABC News: Andrew O’Connor )

Ms Rapaic told the ABC she was walking along the beach with a friend when the incident occurred.

“My friend said, ‘Jac, I think there’s been a shark attack’ and I looked out to the ocean and I could see a pool of blood,” she said.

Ms Rapaic believed two men had been swimming but only one of them had made it back to shore.

“I hugged onto my friend … [we] felt rather traumatised at that point,” she said. “It happened so quickly.”

Russell James was also there when the shark alarm sounded.

People looking toward beach from elevated footpath

Crowds gathered on the footpath above Sorrento Beach.  (ABC News: Mya Kordic )

“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,” he said.

Shark season

The attack is the second reported in WA this week.

Geraldton firefighter Mel Ismail remains in hospital in a stable condition after he was bitten by a shark on Monday.

It comes just a week after Surf Lifesaving WA began its helicopter shark patrols on weekends ahead of the summer season.

Daily patrols are not scheduled to begin until September 26.

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 multiple restaurants and cafes.

Part of the beach once had a shark barrier, which was removed in 2020.

Police officers standing on a beach - photo taken from nearby groyne

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

Barriers are used at Cottesloe, Coogee, Quinns Beach in Wanneroo and Bathers Beach in Fremantle, but some of these are seasonal only and not installed until October.

In the wake of the attack, the City of Joondalup has also closed Hillarys, Whitfords and Mullaloo beaches, according to the WA government’s SharkSmart website.

‘Heartbreaking tragedy’: Premier

In a social media post, WA Premier Roger Cook said he was “deeply saddened” to hear of the attack.

“This is a heartbreaking tragedy and my thoughts are with the victim’s family and loved ones, as well as the first responders who attended the scene,” he said.

Hillarys MP Caitlin Collins, whose electorate includes Sorrento Beach, said the attack was deeply distressing for the community.

“My thoughts are with the victim’s loved ones and everyone who witnessed or is affected by the situation,” she said in a social media post.

A water police speedboat travels in open ocean near the shore.

Water police remain in the area. (ABC News: Andrew O’Connor)

“I want to acknowledge the emergency services, police, surf lifesavers and other first responders who attended the scene and worked to respond to the incident.

“I have spoken with the minister and authorities are continuing to manage the situation.

“Sorrento Beach is a place so many of us love and an incident like this is incredibly difficult for everyone who spends time along our coastline.”

The swimmer’s death is the 24th fatal shark attack in Western Australia since 2000, with 10 of those in the Perth metro area and three occurring this year.

In May, spearfisher Steven Mattaboni died after a shark attack off Rottnest Island, while another spearfisher, Daniel Turpin, died after a shark attack near Albany a few weeks later.