CAMP PENDLETON, Calif. -- A shark attacked a woman wading in the ocean with friends, tearing away part of her upper thigh in the ocean off a popular Southern California beach, authorities and witnesses said Sunday.

The attack occurred Saturday near San Onofre State Beach in northern San Diego County.

"All of the back of her leg was kind of missing," Thomas Williams, one of several witnesses who pulled the woman ashore, told the Orange County Register. "If she didn't receive immediate care, it was life-threatening."

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Williams said the woman was conscious and talking while onlookers used a rubber surfboard leash as a tourniquet to stop the bleeding.

"She was not calm, of course," he said. "But she was coherent."

The beach is adjacent to the Camp Pendleton Marine Base. Marine Sgt. Asia Sorenson said the victim -- a civilian -- was airlifted to a hospital in unknown condition.

The victim was identified by CBS affiliate KFMB-TV as mother-of-three Leeanne Ericson who was at the beach with her boyfriend.

"She was swimming, he was surfing and I guess he heard her scream when he was on the board," family friend Laura Smith told KFMB. "He jumped and dove off the board and went looking for her and found her on the bottom and brought her up on the surf board and paddled in with her and tied the leash around her leg to try to control the bleeding until they airlifted her down to the hospital, but if it wasn't for him she wouldn't have made it. He truly save her life."

Doctor's stabilized Ericson, reports KFMB, but she remains in a medically induced coma.

"There are three little girls that are quite nervous and anxious and it's going to be a shock," said Smith.

The injury was likely caused by a great white or a seven-gill shark, said Chris Lowe, director of the Shark Lab at California State University, Long Beach. Several sharks have been sighted in the area recently.

Nearly a year ago, a woman was bitten by a shark while swimming off Corona del Mar, about 25 miles to the north of the Saturday attack. Experts estimated the shark was at least 10 feet in length, judging from the bite marks, which spanned her chest, hip and shoulder.

Beachgoer Amber Booth was headed to San Onofre to watch the sunset Saturday with her family when a ranger told her the stretch of ocean was closed because of the shark attack.

Booth, who often surfs at San Onofre, said the incident made her worry about her 8-year-old daughter, who boogie-boards often in the area.

"There's so many kids in the water at San O," she said. "You don't really want to think about (sharks) when you're out in the water."

The beach was expected to remain closed until Monday.