Sharks were spotted Thursday afternoon off the coast of Half Moon Bay, according to the San Mateo County Sheriff's Office.
At least four sharks could be seen from the Ritz Carlton hotel to Pillar Point Harbor, sheriff's officials said, and it prompted a warning to beachgoers.
Multiple aircraft along the San Mateo County coast spotted the sharks on their approach to Half Moon Bay Airport, sheriff's officials said.
The sharks were swimming about 40 yards off the shore of Francis Beach.
"My thought was the chances of us seeing a shark were like one in a thousand," said San Carlos resident Bart Selby, who went flying with a friend. "We were up for five minutes, and we saw a shark and then another shark and then another shark."
Selby said he didn't see the sharks displaying any signs of aggression.
Initially, the sheriff's office reported the sharks were Great Whites, but there was no confirmation from marine experts on the type of sharks that were spotted.
State parks will be posting warnings throughout the weekend.