A woman has died after being attacked by a shark reportedly bigger than 5.3 metres off the Perth coast, less than a week after Ben Gerring was mauled near Mandurah.

Key points: Second fatal shark attack in WA in a week

Second fatal shark attack in WA in a week Woman suffered "severe and fatal injuries", police say

Woman suffered "severe and fatal injuries", police say Fishermen claim shark was bigger than 5.3m boat

The woman, 60, was diving about two kilometres off the northern suburb of Mindarie with her 43-year-old diving partner when she was attacked late on Sunday morning.

Three men who were heading out on a fishing trip came to the pair's aid before the woman's companion retrieved her body from the water, between One and Three Mile Reefs.

The woman is believed to have died from her injuries before arriving back at the Mindarie boat ramp near Alexandria Drive shortly before 12pm.

Police Inspector Danny Mulligan said the fishermen had reported seeing a large shark.

"The boat that was in the water was 5.3 metres long, and they say that the shark was longer than their boat," he said.

Inspector Mulligan said the woman's partner had felt "something go past him" while he was diving.

"When he surfaced he saw a commotion in the water and then another boat arrived to pull him out of the water, and then it was noticed that the lady had suffered some severe and fatal injuries," he said.

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"The other boat that was in the water got between the male diver and the shark, and he was able to get back into his own boat and he was able to pull the lady from the water."

He said the pair "regularly dived together in this area".

The Department of Fisheries (DoF) said it was treating the incident as a fatal shark attack, and said it had set three drum lines in the area to fish for the shark.

Earlier, Surf Life Saving WA (SLSWA) sent a tweet at 11:35am saying an unknown species of shark had been sighted 1 kilometre off Mindarie Beach, and there had been a "possible shark interaction".

Local surfer Matthew MacDonald said the woman's diving partner also appeared to be hurt.

"His hand was like taped up, I didn't think anything else was injured," he said.

The City of Wanneroo has closed beaches either side of the Mindarie boat ramp, south from Claytons Beach and Surf Spot and north to Quinns Beach.

The beaches will remain closed on Monday.

Sorry, this video has expired Diver dies after shark attack off northern Perth coast

Second fatal shark attack in WA in a week

It is the second fatal shark attack in WA in the space of six days.

Mr Gerring, 29, died in Royal Perth Hospital on Friday night after losing his leg to a suspected great white shark south of Perth last Tuesday.

The following day a 4.2 metre shark was caught on a baited hook nearby, although the DoF said it was not possible to tell if the animal was responsible.

Mr Gerring was the 13th person to die from a confirmed shark attack in WA since 2000.

There was renewed debate even before his death and the events off Mindarie about the State Government's shark policy, with ministers having elected to place drum lines off Perth beaches in 2013 in response to seven shark deaths.

Premier Colin Barnett last week ruled out a return to permanent drum lines off beaches, but said the Government would continue to hunt and trap sharks it believed were a threat to swimmers.

The State Opposition said it was opposed to catching and killing sharks.