HALF MOON BAY, Calif. » Despite big-wave warnings, two walls of water caught dozens of spectators off-guard and knocked them to a rocky beach as they watched a Northern California surfing contest yesterday, leaving some with broken bones but sparing them from being pulled into the ocean.

Thirteen people swept from a seawall had significant injuries, including broken legs and hands, said California Department of Forestry and Fire Protection Battalion Chief Scott Jalbert. He reduced the official count from the 15 reported earlier in the day but said others treated at the beach for injuries such as scrapes and bruises were not included in the total. At least three of the injured were taken to hospitals.

Jalbert estimated “;a couple hundred”; people were on the seawall at the southern tip of Mavericks Beach when the waves struck, upstaging the surfing competition that draws some of the world's top surfers.

The waves were 6 feet high by the time they hit—”;small, but strong,”; he said.

“;Nobody was swept away into the water. They were just swept onto the beach area pretty hard,”; Jalbert said. “;It's pretty rocky.”;

Additional firefighters had been on the way to clear the beach because of dangerous conditions but arrived too late, he said.

Only after the unexpected large waves swept in during high tide did the National Weather Service post a high-surf warning until 10 p.m. Saturday. The agency previously posted a less severe high-surf advisory.

The surfing contest offers a $150,000 purse, making it the most lucrative big-wave contest in the world, even though it is held only when conditions are prime.

Competitors voted to schedule it because forecasts called for record-breaking tall waves, despite warnings that strong winds could make those breakers dangerously unpredictable.

Chris Bertish, who traveled 21 hours from his South Africa home, won the contest. He had just 48 hours' notice that huge waves were breaking off the coast and the Mavericks Surf Contest was on. Second place went to Shane Desmond of Santa Cruz.

The other top surfers were: Anthony Tashnick, Santa Cruz, third place; Dave Wessel, Kailua, fourth; Carlos Burke Burle, Brazil, fifth; and Kenny Collins, Santa Cruz, sixth.

The two surprise waves knocked out barricades, a spectator platform and a large scaffold holding speakers broadcasting the contest, held in this tiny harbor town 25 miles south of San Francisco along Highway 1.

Marsha Poulin, of nearby El Granada, was at the water's edge minutes before the first rogue wave struck. She said she was concerned organizers were letting spectators get so close to the ocean, given the conditions.

“;Just because they were letting us be here doesn't mean it was safe,”; said Poulin, who left for higher ground just in time.

At least two more rogue waves came through the same area during the high tide, reaching the seawall, knocking down more spectators and sending others fleeing in panic. The subsequent waves were not as large or strong as the first two and did not cause any apparent additional injuries.

Authorities yelled for people to get back from the shore after the waves struck but could not use the public address system because it had been swept away.

“;This is probably the biggest and best contest we've had,”; said Ion Banner, 40, of Half Moon Bay, who was eliminated from the 24-man competition yesterday morning.

“;It was consistently bombing.”;

He and fellow competitor Tim West estimated the waves were 20 to 25 feet measured from the back, with 40-foot faces.