Two adults and two young children are missing from a sailing boat which was reported to be sinking off the California coast in bad weather.
The US Coast Guard has launched a major search of waters south of San Francisco for the group.
Rescue teams have been using aircraft, a patrol boat, lifeboat and cutter, but have not yet found any sign of life.
Lieutenant Heather Lampert said the missing vessel - thought to be named the Charmblow - was about 65 miles off Pillar Point Harbour in Half Moon Bay when the call for help was made on Sunday afternoon.
The group said their 29-foot sailboat was taking on water and that its electronics were failing.
They said they were abandoning ship, but the Coast Guard then lost radio contact with them.
The four people - including two children under 8-years-old - are thought to have made it onto a makeshift life raft.
Local news channel KTVU reported that the victims lacked any real life rafts or survival suits.
They planned to tie a cool box and other materials together to give them a means of floatation until they could be rescued.
The National Weather Service had issued an advisory over the weekend warning boaters of strong winds and rough seas around the Bay area.
Mariners "operating smaller vessels should avoid navigating in these conditions," the advisory said.