SAN FRANCISCO -- On the eve of the Mavericks surf contest, U.S. Coast Guard officials asked surfers off Ocean Beach to come in to shore after strong riptides put at least six riders at risk of being dragged out to sea early Saturday afternoon.

One person may have suffered a shoulder injury, according to Coast Guard Lt. j.g. Joshua Dykman, but he paddled back to shore before rescuers arrived. The rest appeared to be uninjured, and all were safely accounted for as of 2 p.m., Dykman added.

The first call for rescue came around 12:20 p.m., when a group of four surfers was reported missing, Dykman said. Rescuers from the San Francisco Fire Department and a Coast Guard helicopter headed toward the area to search for the group.

A short time later, another surfer who had been caught in the riptide made it to shore by himself, but called 911 when he couldn't locate his friend, Dykman said. The Coast Guard helicopter located the second surfer and was preparing to hoist the person aboard, but the surfer instead made it back to shore, Dykman added.

The Coast Guard also dispatched a 47-foot motor lifeboat to the area, contacting surfers in the water and asking them to paddle in because the riptides were so dangerous, Dykman said.

"The riptide that's going on right now is pulling people out and making it a bigger struggle for them to get to shore," Dykman said.

With waves in the 30-foot range predicted for the Mavericks contest north of Half Moon Bay, pro surfers from around the world scrambled to make it to the Bay Area after organizers said the contest would take place Sunday. The same conditions that make for awe-inspiring curls for the pros, however, present a strong danger to beachgoers throughout the Bay Area.

The National Weather Service has a high surf advisory in effect for Bay Area beaches through Sunday morning. Spectators will not be allowed on the beach at Mavericks, after strong waves caused injuries in 2010.

Follow Daniel M. Jimenez at Twitter.com/DMJreports.