LOS ANGELES - High surf will pound California beaches into the Labor Day weekend, forecasters warned Friday, and crowds celebrating the last summer holiday were urged to watch out for dangerous rip currents.

The National Weather Service extended high surf advisories through Sunday night, warning that 6- to 8-foot waves, with occasional 10-foot sets, would hit the coast from San Francisco to San Diego.

Beachgoers were urged to swim only near lifeguard towers - or to stay on the sand.

"Have a good time watching the waves but stay out of the water if you're not experienced," National Weather Service forecaster Eric Boldt said.

The rough surf was caused by the swell from a powerful storm in New Zealand, where it is winter.

"It had 50-foot waves down there when it was going at its peak. The energy came up here," Boldt said.

Roughly 10-foot waves forced the closure of two Orange County beaches after damaging a wooden boardwalk and some steps at Capistrano Beach in Dana Point, and crashing onto the parking lot of Aliso Beach in Laguna Beach.

Orange County Parks officials will monitor ocean condition today to determine whether they can reopen the beaches for the holiday weekend, agency spokeswoman Marisa O'Neil said.

On Thursday, the powerful surf probably forced a smuggling boat to crash on a Southern California beach where more than 500 pounds of marijuana washed ashore, authorities said.

State park rangers found the abandoned boat split in half on rocks near Point Mugu, Calif., northwest of Malibu, Calif., said Lindsey Templeton, a superintendent for the park system said.

Waves reaching 6 feet to 9 feet and "probably a lot of misjudgment by the cartel operating the boat" led to the crash, Templeton said.

A body-boarder who vanished Wednesday evening at a beach near Huntington Beach might have been caught in a rip current. The search for Jowayne Binford, 24, of Long Beach, Calif., was suspended on Thursday.

Lifeguards rescued two dozen people on Thursday on Los Angeles County beaches from Marina del Rey north to Topanga, said Capt. Angus Alexander. High surf prompted officials to move several lifeguard towers farther inshore, he said.

Waves reached shoulder to head height on Friday morning, but the biggest concern was not atop the surf but below it.

The heavy surf chewed up the sandy bottom, creating potholes that can dunk unwary swimmers and contributing to dangerous rip currents.

"People who will be in waist-deep water one moment may be in a hole where they can't stand up the next minute," warned Huntington Beach lifeguard Lt. Mike Baumgartner.

The holes and heavy swell also create dangerous seaward-flowing rip currents.

"That probably kills more people in Southern California than any other phenomenon," said Boldt, of the weather service.

Swimmers can quickly become exhausted and drown if they fight the current instead of swimming parallel to the shore until they are out of it.