Note: Our coverage of the dangerous surf conditions has moved here.
Streets along Ventura's beach communities were coping with several feet of water, leading multiple vehicles stranded. Lifeguards had to perform multiple rescues, in most cases of people who had gathered to watch the big waves from the sand but were caught up unexpectedly in them.
One video showed bystanders pulling a lifeguard out of the water with his arms after he apparently became exhausted trying to fight the powerful tow.
Another video showed a massive rogue wave breaching a low wall in Ventura, sending onlookers fleeing and sweeping up several of them in water. Officials say eight people were treated at local hospitals for injuries.
Rogue wave sends people fleeing along Ventura shoreline
Rogue wave sends people fleeing from beachside road in Ventura
In another video, a man went paddleboarding with his daughter along a flooded street.
People who live in affected communities can't recall seeing waves this size at least in the recent past.
"The waves were big," said Ventura resident Brian Scott. "I mean, I'm a water guy. I sail, scuba dive. These were 15+ foot waves this morning at high tide. Never seen that. We've been here for 10 years."
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A high surf advisory went into effect at 4 a.m. Thursday and will last through 10 p.m. Saturday.
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The National Weather Service says some local areas could see waves up to 15 feet high. The Ventura County coast, and Hermosa, Manhattan and Palos Verdes beaches are expected to see the most significant impacts.
The state's central coast is also expected to be hit hard.
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Several cars were seen stuck on a flooded street near the beach in the area of Seaward and Zephyr. Lifeguards were warning people who had gathered to watch the big waves that they needed to move farther back from the water.
In Oxnard, streets near the beach were similarly flooded and several cars were trapped as well. All Oxnard public beaches will be closed Friday through Sunday due to the high surf advisory.
Officials say flooding is possible in some low-lying areas. In Newport Beach, residents were warned about the conditions and sand berms were replenished.
City officials said crews would be monitoring water levels and will pump water out if needed. Residents can pick up sandbags from the city's Corporation Yard at 592 Superior Avenue from 7 a.m. to 3 p.m. Thursday and 7 a.m. to noon on Friday.
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Meanwhile, Los Angeles County beachgoers are urged to speak with lifeguards before going into the water.
Despite the advisory, many surfers turned out at Seal Beach ready to catch some waves early Thursday morning.
"Seal Beach is kind of like a stadium. Everyone likes to come here. It's an easy, makeable wave... and everyone loves to be (here)," said Jeff Brockman.