Authorities responded to reports of a shark attack at Lovers Point Beach, in Monterey Bay, around 10:30 am local time.
A male swimmer was found with major injuries. He has been transported to hospital, an update on his condition has not been provided.
In a statement Pacific Grove Police Department thanked "Good Samaritans" who rushed to help the swimmer.
"(They) took immediate action and personal risk to assist," they wrote.
The beach at Lovers Point and Sea Palm turnout has been closed and will remain closed until Saturday, June 25, 2022.
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The species responsible has not been identified, but great white shark populations are booming in the area.
Monterey Fire Department, with the assistance of the Seaside Fire Department, deployed a drone to conduct an aerial search of the area for the animal.
"At the time of this release, there have been no additional sightings," police said in a statement.
"The area will continue to be monitored during the closure."
This attack comes months after a bodyboarder was fatally mauled by a great white shark in Morro Bay on Christmas Eve.
More to come…