Authorities in California believe a great white shark attacked and killed a swimmer training in the ocean with a group of triathletes.

Interactive: Shark Attacks Common?

A deputy fire chief said Friday 66-year-old Dave Martin was swimming when the shark apparently "came up, bit him and swam away."

The man was taken to a lifeguard station for emergency treatment but was pronounced dead at the scene. The man's injuries crossed both thighs.

A family friend said club members had been meeting at the beach for at least six years and never had seen a shark. He also said Martin may have bled to death before he left the water.

Swimmers were ordered out of the water for a 17-mile stretch around the attack site.

Helicopters were scouting to see if the shark was still in the area.