A wooden skiff believed to have been ferrying migrants toward the US capsized in stormy seas near San Diego, leaving at least four people dead and four hospitalized, the Coast Guard said Saturday.

The US Border Patrol found the vessel in the surf off Imperial Beach late Friday night. Six people were found on the beach just before midnight, one of whom was pronounced dead and another who was rescued after being found under the boat.

About two hours later, authorities received a report of someone in the water near Imperial Beach Pier. A Coast Guard crew responded and found three people in the ocean, all dead.

The Coast Guard said Saturday that it was continuing to search for others who may have been on board.

Several of the survivors claimed Mexican nationality, while others remained unidentified, the agency said. One person was turned over to the Department of Homeland Security.

“Our crews and partner agencies responded immediately, but this case demonstrates the severe risks posed to aliens attempting to enter the United States by sea in unstable vessels,” said Coast Guard Capt. Robert Tucker, Sector San Diego commander.

A strong storm system hit Southern California over the weekend, prompting warnings of flash flooding and mudslides. The vessel was a panga — single- or twin-engine open fishing boat that is also commonly used by smugglers.