A man has been killed by a four-metre shark at Horseshoe Reef off Rottnest Island.

Frantic attempts were made to save the 38-year-old, who was pulled onto a boat and taken to shore, where he was attended by paramedics on a wooden jetty at Geordie Bay.

7NEWS vision showed a dozen people were huddled around the wounded man, who was partly covered by a blue blanket.

Police were also at the scene, with a water police vessel moored nearby.

Emergency services were scrambled just before 10am. An RAC Rescue helicopter was sent to the incident.

WA Police said it was advised of a possible shark attack off Rottnest at 9.55am.

“A 38-year-old man was in the water at Horseshoe Reef when he was believed to have been bitten by a shark,” a police spokesperson said.

“The man was conveyed by vessel to shore, where he was met by SJA WA paramedics. Sadly, the man was unable to be revived.

“WA Police will prepare a report for the Coroner.”

The Department of Primary Industries and Regional Development said it was alerted to the shark attack at 10.03am.

“DPIRD is working with WA Police to coordinate responses,” a spokesperson said.

“A DPIRD patrol vessel will be on the water monitoring the area.”

Horseshoe Reef is north of Marjorie Bay, at the west of the island. DPIRD had earlier reported the incident occurred at Geordie Bay.

Boyd Fraser, staying on the island for the long weekend, said he planned to go snorkelling but saw a report about the attack and had changed his plans.

He said the area was “sharky” and he wouldn’t be game to swim there.

“I wouldn’t snorkel that far (out). How horrific, what a horrific way to go,” he told The West.

“Poor fellow.”

Staff at the Geordie Bay General Store assumed the emergency response was for a child they sought assistance for after he fell off his bike.

Unbeknown to them, tragedy was unfolding a short distance away.

Visitors to the island described the incident as “horrible” and some did not want to discuss what happened in front of their children.

Staff at Geordie’s Cafe and Art Gallery said they didn’t realise what was unfolding around the corner.

A patron said despite being at the cafe, she hadn’t heard anything about a fatal shark attack.

After being told, she decided to stay out of the water for the duration of her visit.

She was also surprised there had been no circulation of information across the island communicating news of the fatal attack.

Another couple only found out because someone in Perth called to ask if they were okay.

A couple that swim at Geordie Bay every day said they would avoid swimming for the foreseeable future.