A CHP chopper spotted the animal in the water at about 12:30 p.m. Friday. Officials say it appeared to be a great white shark about 12 feet long.
Pacifica Police quickly posted warning signs near the beach.
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"Gotta be cautious," said Jouilani Tavita of Daly City, who kept a close eye on her kids. "I'm definitely going to keep us on the sand. No swimming."
Police tweeted out the warning and alerted neighbors on NextDoor.
Officials say there was no aggressive behavior by the shark reported and asked beachgoers to be careful and aware of their surroundings at the beaches in Pacifica.
Hours later, SKY7 spotted what looked like the same shark swimming off the coast, now only hundreds of feet away from surfers.
Surfer Chris Hamilton is relieved the shark never got too close. "To see one that close to where I surf and live -- not good."
Other surfers didn't care. "Whatever," one said.
Shark experts say great white sightings are rare but not uncommon in the Bay Area. They're not usually spotted until September or October when the Pacific gets warmer.
"What usually might be around this time of year is a sub-adult," said Professor Barbara Block of Stanford Marine Sciences. "A younger shark hunting for a marine mammal."
Block says the shark spotted in Pacifica wants to travel and could be 80 miles away by the weekend.
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