A swimmer went missing off the California coast in a reported shark attack. Officials say shark attacks in the area are extremely rare.

• A swimmer went missing off the coast of California after an apparent shark attack on Sunday.
• Three friends were swimming when one of them spotted blood in the waters, an official told Insider.

A man went missing while swimming off the coast of California after an apparent shark attack that witnesses said left a pool of blood in the waters, officials told Insider on Monday.

The incident unfolded Sunday just before 11 a.m. at Marin County's remote Wildcat Beach in the southern part of the Point Reyes National Seashore nature preserve.

Three friends were swimming off the beach when one of them suddenly spotted blood in the waters around them, prompting that person to "scream" for the group to get back to the shore, witnesses told authorities, Sgt. Adam Schermerhorn of the Marin County sheriff's office told Insider.

"Only two of the three friends returned to the beach itself," Schermerhorn added.

Authorities didn't immediately release the identity of the missing man, who KPIX-TV reported is in his 50s.

A spokesman for the US Coast Guard, petty officer Hunter Schnabel, told Insider that agency was treating the incident as a missing persons case.

In the aftermath of the ordeal, members of the Coast Guard, National Park Service, Marin County Sheriff's Office, and the Marin County Fire Department launched a search and rescue operation by air, land, and sea.

But part of that search was suspended on Monday morning.

"The US Coast Guard suspended its search in the frigid waters this morning, but a ground search is being conducted by first responders from the NPS, the Marin County Sheriff's Office and the Marin County Fire Department, and the Stinson Beach Fire Department," the National Parks Service said in an advisory, according to KRON-TV.

Officials say shark attacks in the area are rare

Marin County firefighters told KPIX-TV that shark attacks are extremely rare in the area where the incident happened.

"To my knowledge, yeah, this could be the first fatal shark attack" in the Marin County area, "but we're hopeful that he'll be found," senior captain Ben Ghisletta of the Marin County Fire Department told the news outlet.

The chances of being attacked and killed by a shark are low at one in 3.75 million, Insider has previously reported.

But California has been ranked among the few shark attack hot spots around the world.

Schermerhorn told Insider that people who used to surf in the waters off Wildcat Beach years ago remembered the area as a breeding ground for seals that was "highly infested with sharks."

"I don't know that it currently is or if it's seasonal, but I know that their experience when they used to surf out there years ago was that it was what they described as being a seal breeding ground, so there was lots of sharks always in the area," Schermerhorn said.