The US Coast Guard has called off a search for a missing swimmer almost 24 hours after their disappearance following reports of a shark attack.

The person was reported missing on Sunday morning near Point Reyes National Seashore, north of San Francisco, prompting a multi-agency investigation.

A spokesperson from the Coast Guard confirmed that searches by sea and air had taken place overnight, but that operations had now been halted pending further developments.

The swimmer was last seen Sunday at Wildcat Beach, part of the Point Reyes National Park.

Petty Officer Hunter Schnabel told The Independent that the Coast Guard had been contacted at around 10.40am on Sunday.

“We received a report that they had witnessed someone getting attacked by a shark and that they were now missing,” he said.

“At this time the Coast Guard launched assets by sea and air and searches continued throughout the day yesterday and overnight.”

Mr Schnabel said that the searches had been called off at around 9am local time on Monday.

He added that the next of kin process was underway and that searches would not resume unless “relevant information” emerged that would lead the agency to believe there was “a reason to continue” with efforts.

Personnel from Point Reyes National Park Service, Marin County/ Stinson Beach Fire and four helicopters had been involved in the search.

Samantha Edell, who was present at the time of the incident, said that her son had heard “screaming” and that a group of people had gathered by the water.

"They told me that their friend was out swimming, and he was attacked by a shark. I said, ‘How bad is it?’ They said he never came out of the water," she told the San Francisco Standard.

Ms Edell said that the group in question had been backpacking in the area after having previously attended a wedding together.

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