An Australian teenager was killed in a shark attack on Tuesday while surfing in what lifesavers said were dangerous morning conditions, prompting authorities to close several beaches.

The 16-year-old boy was surfing with a friend at Ballina, on the north coast of New South Wales state, when the shark bit his upper leg and body. The other boy told police he saw a dark shape, then the water filled with blood.

"One of the boys indicated that he was in trouble to his mate. His mate went over to help and found that he had been attacked," said Surf Life Saving NSW spokesman Craig Roberts.

"He was unconscious and the lifeguards and ambulance officers had some severe haemorrhage to deal with," Roberts said. "Unfortunately the boy died due to his injuries."

Local lifesaver Stephen Leahy said the attack occurred 50 metres (164 feet) from Lighthouse Beach around 8.30 a.m. (11.30 p.m. British time) and followed a day of heavy rain, which had reduced visibility.

"The water was dirty and murky, and it is one of the things which we would always say, that's not a good time to go swimming," Leahy told Australian radio.

Beaches in the area were closed to swimmers after the attack, he said, but a search for the still-unidentified shark had been abandoned because of poor visibility in the water.

The beach, just north of a local river mouth, is popular with surfers, but is also a frequent feeding area for sharks.

Lifesavers, who earlier this year had stepped up patrols with jet skis and helicopters during the height of the Australian summer, had not started patrols when the attack occurred, Leahy said.

Sharks are protected in Australia and attacks on humans are relatively rare, despite the country's huge coastline. Around 42 percent of attacks involve surfers or windsurfers, according to the U.S.-based International Shark Attack File.

Australia had 12 shark attacks in 2007, none of them fatal, among 71 shark attacks worldwide that year.