Tributes have flowed for an Australian father-of-two who was killed after a shark attack on Saturday in Western Australia (WA).

Steven Mattaboni, 38, was attacked by a 4m (13ft) shark around 10:00 local time at Horseshoe Reef, north-west of the popular Rottnest Island near Perth.

He was spearfishing with friends about 1km offshore when he was bitten on the lower leg in what police described as a "horrific" attack. His friends rushed him back to shore but emergency services were not able to revive him.

His wife, Shirene Mattaboni, described him as an "incredible father" to the couple's two young daughters, saying he was an "avid fisherman" who "lived and breathed the ocean".

"Steven was a devoted father to our two beautiful daughters - one who turns three next month and our four-month-old baby," she said in a statement, adding the family's "hearts are irrevocably broken".

She described her husband as "fiercely loyal, endlessly generous, and the kind of man who would give you the shirt off his back".

"The world has lost a truly one-of-a-kind gentleman, and our daughters have lost an incredible father far too soon."

The Kingsley Amateur Football Club in Perth's northern suburbs also paid tribute to Mattaboni, who played for the club and was a "much loved friend to many".

"Mattas was one of the most genuine people you could meet," the club wrote in an online post.

"He had a smile and presence that could light up a room, and he will be remembered fondly by all who had the privilege of knowing him."

The president of the Australian Underwater Federation - the peak body for spearfishing - said he was saddened by Mattaboni's death.

"My heart goes out to his family, the club members and the people who were supporting him out on that dive," Graham Henderson told the Australian Broadcasting Corporation (ABC).

"Spearfishing... we understand it is a dangerous sport in some way, but we try to mitigate those risks. Any competitions we have, we have safety boats in the area and we often put drones up to spot sharks.

"But of course when people are doing it recreationally... that is probably when they are most vulnerable."

Earlier, WA Police Sergeant Michael Wear said Mattaboni had been about 20m from his boat when he was bitten.

"The friends have witnessed the horrific event," he told local media.

Later, the state's police minister praised the efforts of the man's friends and first responders who tried to save him.

"I want to acknowledge the diver's friends who played a critical role in doing the best they could to bring [him] back to shore," Reece Whitby told local media on Saturday.

"They all witnessed a very confronting, disturbing and tragic scene," he said.

The WA Department of Primary Industries and Regional Development confirmed it had received a report about a man being bitten by a four-metre shark.

WA Police will prepare a report for the coroner.