UPDATE: Two people have reported spotting a 3m shark circling their boat near Garden Island, a day after a 20-year-old woman was attacked by a white pointer in the area.
At about noon it was reported that a shark estimated to be about 3m long circled the boat, before quickly disappearing.
Fremantle Volunteer Sea Rescue went out to look for the shark but could not spot it.
Water police said the people were not sure what sort of shark it was.
The victim of the shark attack, Elyse Frankcom, is recovering in Royal Perth Hospital after being bitten on the buttocks and thighs.
News of today's shark sighting came after a popular open water swimming event due to kick off in Rockingham today was cancelled because of the attack.
Swimming WA cancelled the first round of the Open Water race series – a six-part event from October to January involving ocean swims of 1.25km, 2.5km and 5km – after consultation with its water safety advisors and local authorities.
"Swimming WA takes the cancellation of an event very seriously, thoroughly evaluating each case individually," Swimming WA said.
"In this instance we deem our actions are appropriate considering the close proximity of the shark attack to the event’s location."
The event may be rescheduled.
The victim of the attack was diving about 300m off the north-eastern end of Garden Island when the attack happened at about 1pm. She was hosting a swim-with-the-dolphins tour for Rockingham Wild Encounters.
The attack happened near the Garden Island Ammunitions Jetty, west of Rockingham.
It is understood the shark attacked from below and the woman was in the centre of a group of divers.
A man who was on the tour with Ms Frankcom is understood to have pulled on the tail of the shark, which let go of her.
The man then brought Ms Frackcom back to the surface.
She was taken by boat to the island and treated at the navy medical centre before St Johns Ambulance officers arrived at the scene. She was then airlifted to Royal Perth Hospital by the RAC helicopter.
The woman’s injuries are described as serious but she remained conscious after the attack and told rescuers she believed the shark had been a white pointer - she was not sure how big the animal was.
It is understood she underwent surgery for her injuries last night.
Last month Ms Frankcom wrote on her public Facebook page that she kept hearing about three great white sharks:
"I get it (people) haha! If i get attacked or die, at least i die happy & doin the thing i love :) time 2 use our shark shields soon maybe..."
Ms Frankcom also described the joy of her job swimming with dolphins in a later post.
"The look they give u is so deep, like an instant bond... And being so close actually swimmin with them jst leaves me speechless," she wrote earlier this month.
Water police spent yesterday afternoon in the area warning other divers of the attack and telling boat users to be on the look out for the predator.
Rockingham Volunteer Sea Rescue are also on alert and in the area. The Surf Life saving helicopter searched for the shark for several hours and will be back in the air tomorrow in another bid to track the predator.
Regional manager for the Department of Fisheries Tony Cappelluti said fisheries officers were on standby should the shark be spotted.
If found it would be tracked until it went far enough off shore to no longer present a danger.
Mr Cappelluti said shark attacks tended to be random and he did not think they were necessarily becoming more common.
“This time of the year to get a lot more people in the water so the chances of interacting with a shark increase,” he said.
“We can’t really say that there are more sharks out there, just more interactions.”
Chris Peck from Surf Life Saving WA said his organisation had no plans to close any beaches in the aftermath of the attack.
He said the shark attack appeared to be diving related and therefore was not within his organisation’s jurisdiction.
He said he understood the attack had occurred some distance from the shore.
Lou Hynd from the water police said the woman had been wearing a wetsuit and the dive charter had been using a form of shark repellent. He said the woman was from Rockingham.
He warned divers using Cockburn Sound today to be cautious following the attack.
The attack was the first in WA waters since the death in August of 31 year-old surfer Nicholas Edwards, who died after being bitten by a white pointer near Gracetown.
In December 2008, Brian Guest was taken by a shark in Warnbro Sound, a short distance away from today’s attack.
Mr Guest, whose body was never recovered, was taken by a 4.5m white pointer about 7am on December 27, while diving for crabs with his son Daniel about 50m offshore.
Witnesses on shore described seeing “a huge creature” with a dorsal fin “one metre in height”.
A three-day search turned up the remains of a black and blue top identified as Mr Guest’s.
An Esperance couple missing for nine days in remote bush has been found alive.