As a crowd watched the high surf at the end of an avenue in Ventura, California, a "rogue" wave crashed over the seawall, flooding the area and carrying people and vehicles up the street.
The wave sent eight people to the hospital on Thursday, a spokesperson for the Ventura County Fire Department said on social media.
Cities along the California coast were warning residents that the rough waters caused by a Pacific storm this week can turn quickly into dangerous waves.
"Stay away from rocks, jetties, piers, and other waterside infrastructure," the National Weather Service in the Bay Area said on social media. "Never turn your back to the ocean!"
NWS officials issued a high surf warning that was in effect until 3 a.m. Friday in the Bay Area. They warned of "very dangerous" waves that could reach as high as 40 feet in some spots.
The highest surf was expected Thursday, but conditions were still forecast as dangerous and were expected to continue into Saturday. A high surf warning remained in place for Southern California into Saturday night with waves 15 to 20 feet, and local sets reaching 25 feet.
The rain is forecast to start Friday morning in the northwest and is expected to reach the Bay Area by the afternoon. It could impact evening travel around San Francisco. The storm also comes with wind, especially near the coast, where gusts could reach 50 mph Friday.
Santa Cruz Fire Department officials issued an urgent advisory on Thursday, saying, "The big surf we have been talking about is here! Please help us keep you and our teams safe!"
The Southern California city closed Santa Cruz Wharf, along with Main Beach and Cowell Beach. Low-lying areas along West Cliff had been flooding, with debris "crashing on shore with big waves," officials said.
Waves near Santa Cruz were expected to be 25 to 30 feet, the National Weather Service said. The service warned of rip currents, storm surges and "sneaker" waves in the area.
"We urge everyone to remain INDOORS and away from the coastline for your safety," the Santa Cruz Fire Department said on social media on Thursday.
In Ventura County, where a wave sent eight to the hospital, some public beaches were closed. The city of Oxnard said it had closed its beaches through Sunday.
Fire officials in the county spent Thursday night using heavy equipment and bulldozers to construct a berm along the beaches to guard against high surf.
"The finished berm is about seven feet high and about a mile in length, running from San Pedro St. down to Greenock Lane," a spokesperson said.