A huge wave swept away spectators watching a surfing contest yesterday in northern California, causing broken bones and other injuries to people standing on a seawall.

Brendan Reidy, a contest staff volunteer helping with the rescue effort, said authorities do not believe anyone is missing following the incident.

He said several people had broken bones and many others had cuts and bruises.

At least seven people were removed in emergency vehicles from the beach, which was scattered with other spectators being treated for their injuries. Witnesses said the wave knocked out a large scaffold holding speakers broadcasting the contest.

"It just came out of nowhere and wiped us all out," said Pamela Massette. Her left hand and left knee were scraped and bleeding and she was wet from head to toe.

Brandon Snider was also injured. He said everyone's concentration was on the contest when a 5ft-6ft wave "wiped out the entire seawall".

He said it is unclear how many people were on the seawall, but he believes some were seriously injured.