The search for a man feared taken by a shark off a West Australian beach has so far failed to find him.
Brian Guest, 51, was snorkelling for crabs with his son off their local beach near Rockingham, south of Perth, when he suddenly disappeared from view shortly after 7am on Saturday.
His son Daniel, 24, swam to shore and raised the alarm.
Witnesses told police they saw flashes of fins in the area and the water was coloured by blood.
"Something very traumatic and pretty violent has happened there and we are treating it as a probable shark attack," acting Inspector Mark Valentine said.
"There was lots of talk among witnesses at the incident location about seeing fins in the water but we can't yet say whether there was definitely a shark out there, though in all probability that's what it is."
The beach was immediately closed as police, marine rescue patrols and three helicopters mounted a huge search for the missing man.
The three emergency service aircraft, 10 boats and divers conducting a grid search by late Saturday afternoon had found nothing.
It was the second fatal shark attack in Australia this year.
In April, surfer Peter Edmonds, 16, died after being attacked by a shark at Ballina, on the NSW north coast.
