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Representative image. Credit: Pixabay / valdeck

The U.S. Coast Guard has initiated a search operation for a missing swimmer believed to have encountered a shark off a California beach near San Francisco.

According to Coast Guard San Francisco Public Information Officer Grace Patton, authorities were alerted to the incident by a witness near the Wildcat Beach region of Point Reyes National Seashore on Sunday.

"We have received reports of a shark attack, but we have not yet confirmed it," Patton told Fox News Digital on Monday.

The swimmer went missing after being last spotted in the vicinity of Wildcat Beach at Point Reyes National Seashore.

Point Reyes National Seashore, as per the National Park Service website, boasts approximately 80 miles of shoreline, including extensive stretches of beach.

On Sunday, search efforts were carried out collaboratively by personnel from the Marin County and Stinson Beach fire departments, the National Park Service, the U.S. Coast Guard, and other relevant agencies. According to the National Park Service, the search team utilized two helicopters in their efforts, NBC News reported.

Meanwhile, CBS San Francisco reported that Marin County firefighters discovered that three males had been swimming when one of them was attacked by a shark.

The station further reported that the remaining swimmers informed first responders that they had been swimming between 25 and 50 yards from the shore, noting the presence of a significant amount of blood in the water.

"Regrettably, despite conducting a comprehensive search covering 21 square nautical miles under ideal conditions, we have not located anything. Our objective remains to persist in the search," U.S. Coast Guard Lt. Rachel Davis iaid in an interview with CBS San Francisco on Sunday.

Marin County Fire Department Senior Captain Ben Ghisletta told CBS San Francisco that this could be the first fatal shark attack in the area, but expressed hope for the missing swimmer's recovery.

The California Department of Fish and Wildlife reports that there have been 210 shark attacks and events off the coast of California since 1950, 15 of which have resulted in fatalities. The most recent shark encounter was documented on Aug. 22 at Bean Hollow State Beach in San Mateo County. The victim was kayaking and was unharmed.