Crews on Saturday were searching by air and sea for the body of a 60-year-old man who was last seen in the waters off of Salt Creek Beach in Dana Point, authorities said.
The search began after lifeguards received a report about 11:33 a.m. that the man had gone missing, according to the Orange County Sheriff's Department.
"It just escalated really quickly," according to witness Dominic Gibson, who said he was in the water when the rescue attempt began. "They had the lifeguards go out, and then they had the jet skis, three boats and two helicopters. They didn't find anyone."
The operation became a recovery effort about 1:03 p.m., the Sheriff's Department said in a statement.
A number of agencies were assisting in the search, including the U.S. Coast Guard, the Orange County Fire Authority, the Long Beach Fire Department and Newport Beach lifeguards.
The Coast Guard dispatched at least one helicopter and boat, while a snorkel team from the Sheriff's Department was also looking for the swimmer.
"We're in the business of preventing this from happening as much as possible, but the ocean's an inherently dangerous place," O.C. Lifeguards Chief Jason Young said of the man's disappearance. "It can happen to even experienced watermen. Our lifeguards understand that, but it's difficult. We never like to lose anybody."
The incident comes amid a high surf advisory that was issued by the National Weather Service.
The weather service had also warned swimmers and surfers to watch out for dangerous rip currents along the Southern California coast this weekend.
"Typically, we say, if you're not an expert or very experienced surfer or swimmer you should not enter the ocean in these conditions," Young said.
KTLA's John A. Moreno contributed to this report.