At least three people have died during a yacht race in Newport, US, weeks after another fatal accident off California.
US Coast Guard boats are looking for a fourth crew member from the yacht Aegean.
Race organizers the Newport Sailing Association said the wreckage indicated the yacht collided with a ship much larger than the 37-foot vessel.
On Thursday the Coast Guard suspended yacht racing around San Francisco after a fatal accident earlier this month.
Five people died when powerful waves threw their yacht onto a rocky island. Three others survived the accident.
The Coast Guard said the suspension was to see whether changes were needed to improve race safety rules.
Race officials said the Aegean disappeared from their tracking system early on Saturday a few miles off the coast near the border between the US and Mexico, an area close to where the race route crossed shipping lanes.
Two of the dead have been identified as William Reed Johnson from California and Joseph Lester Stewart from Florida. The identity of the others on board has not been released.
Eric Lamb, one of those involved in the search of the wreckage, said small pieces of debris from the boat were scattered over a wide area.
“We have pulled a lot of boats off the rocks over the years and boats that hit the rocks, they don’t look like that. This was almost like it had gone through a blender,” he told Associated Press.
Other sailors point out that it is possible for a large ship to hit a yacht without the crew being aware of the smaller craft.
The coastguard said there was good visibility and moderate ocean swells at the time. An official at the sailing club organizing the race suggested that in light winds the yacht may not have been able to get out of the way of the larger vessel.
Other participants in the race said they saw a tanker or heard warnings on their radios.
“This has never happened in the entire 65 years of the race that I’m aware of,” the commodore of the Newport Sailing Association Chuck Iverson told the Associated Press news agency. “We’re all shocked by this whole event.”
The 125-mile (202 km) race began at Newport on Friday, with boats arriving in Ensenada on Sunday.
In March two sailors were injured off the North California coast in a round-the-world race when a huge wave overwhelmed their boat.