A shark attacked a 13-year-old who was diving for lobsters at a beach in California early on Saturday morning, leaving him with traumatic injuries to his torso, the authorities said.

The teenager, identified in an online fund-raising site as Keane Hayes, was screaming when other lobster divers heard him and quickly came to his aid.

Keane was in serious condition at Rady Children’s Hospital in San Diego, a hospital spokesman, Carlos Delgado, said on Sunday. The teenager was conscious and speaking when he was airlifted to the hospital from Beacon’s Beach in Encinitas, Calif., said Larry Giles, the captain of the lifeguards.

The attack happened about 200 yards from the shore in about nine feet of water, Captain Giles said. The authorities believe the shark was 11 feet long but have not found it. The species of shark was not yet known.