ADELAIDE - Friends watched two great white sharks attack and kill their 18-year-old surfer mate off an Adelaide beach yesterday.
Nick Peterson was taken by the sharks while surfboarding behind a boat at West Beach, about 10km west of Adelaide city centre.
One shark attacked Mr Peterson after he fell from the surfboard, tearing him in half, authorities said.
The other shark took the youth's remains.
It was the second fatal shark attack in Australian waters in a week.
A Great Barrier Reef spearfisher died last Saturday after a shark bit his leg.
Police and South Australian emergency services said there had been no sign of the Mr Peterson or the sharks since the attack, which happened about 3.30pm.
SA Sea Rescue Squadron spokesman Frasier Bell said one of the white pointers was believed to be about 5m long and the other about 4.5m.
The attack happened 200m to 300m offshore on a hot day at a crowded beach. "He fell off the surfboard and the shark appeared and took him," Mr Bell said.
"It tore him apart."
Mr Peterson was being towed by a boat containing three 16-year-old friends, two of whom witnessed the attack.
The four, all from Adelaide's western suburbs, had been on the water for just 30 minutes before the attack occurred.
"They were just boys having a good time, the weather was perfect and they were just out doing what young lads do," Mr Bell said.
The teenagers tried in vain to rescue their mate.
"They tried everything they could think of but unfortunately the sharks had taken him by that stage.
"They're in deep shock. They're wrecks. You can just imagine what the victim's parents are going to go through."
Chief Inspector David Lufty of South Australia police said beaches in the West Beach area would be closed as the search for the killer sharks continued.
He said that in the two hours immediately after the attack no items of significance were found, lending weight to the belief that Mr Peterson was killed instantly.
Mr Bell said there had been recent reports of shark sightings off Adelaide's metropolitan coast, with the sea squadron issuing a shark warning a couple of weeks ago.