By Artemis Moshtaghian and Dakin Andone, CNN

(CNN) -- A 13-year-old boy who was attacked by a shark early Saturday is in serious condition, downgraded from the critical condition he was in originally, according to a spokesperson from Rady Children's Hospital in San Diego.

The boy was attacked while diving for lobsters in waters off Encinitas, California, near San Diego, authorities said.

The boy suffered traumatic injuries to his upper torso and was taken to a hospital, Encinitas lifeguard Capt. Larry Giles told reporters.

Encinitas is about 25 miles north of San Diego.

The attack happened before 7 a.m., about 150 to 200 yards from Beacon's Beach, Giles said.

Several people were in the water diving for lobsters, he said, because it was the opening of the season for catching the crustaceans. Three good Samaritans heard the boy's cries and helped bring him ashore using a kayak, Giles said.

Lifeguards had been on duty early Saturday because of two nearby events, and the response to the attack was "very short," Giles said.

"The lifeguard was within a quarter-mile of the incident with a lifeguard truck and arrived on scene and started providing first aid right away," he said. The lifeguard was an emergency medical technician, Giles added.

Paramedics arrived soon after, and the boy was taken to the hospital. He was conscious and talking on the beach, Giles said, as well as on his way to the hospital.

Chad Hammel said he was one of the people in the water who helped.

Hammel said he thought the boy was just excited when he first heard him shouting.

"And then I realized that he was yelling, 'I got bit! Help, help,' " Hammel said.

He didn't realize the extent of the boy's injuries until he and a friend put him on their kayak.

"Once we got him on the kayak we could really see what happened," Hammel said. "And his whole clavicle's ripped open; you could see the ball and socket joint and everything."

The beach adivsory is expected to continue until 7 a.m. Monday, "unless there are other shark activities in the area," Lois Yum, city of Encinitas spokesperson, said in a press release.

Nearby beaches between Ponto Beach and Swami's Beach will be closed for 48 hours after the attack, Giles said. There has been no shark activity in the area since the attack. One scheduled surf event was canceled.

Giles said there was a nonfatal shark attack earlier this year at Camp Pendleton, north of Encinitas.