Two Irish men are missing after they were swept overboard from their yacht off the coast of San Francisco on Saturday.
Two other sailors are also missing after powerful waves battered their boat during a yacht race, tossing it into rocks around islands off San Francisco, officials said.
The body of a fifth sailor has been recovered from the sea.
A spokeswoman for the Department of Foreign Affairs said the Irish consulate in San Francisco was liaising with the US coast guard and providing assistance to the missing men's families.
The missing Irish sailors have been named as Alan Cahill, who has been living in Tiburon in California for many years and his friend Elmer Morrissey from Co Cork. It is believed that Mr Morrissey was studying in the US for the past year.
Mr Cahill is understood to be a married father-of-two and an experienced yacht race sailor, originally from Blarney, Co Cork.
The Coast Guard made the decision to stand down the search after covering more than 5,000 square miles of ocean over more than 30 hours. "An air and sea search was suspended indefinitely around sundown and we will not go back tomorrow," spokesman Caleb Critchfield said.
"We kept searching 12 hours past what we consider the survivability window. We extend our deepest sympathy and our hearts go out to the family and friends of the victims," he added.
The vessel Low Speed Chase, a 12-metre racing sailboat with a crew of eight, was one of 49 yachts competing on Saturday in a race around South Farallon Island, part of a rugged, sparsely populated chain offshore from San Francisco.
Officials said trouble began as the vessel rounded South Farallon Island on Saturday afternoon. A large wave initially swept four crew members into the ocean and when those remaining aboard tried to turn the craft around, another wave pushed the boat onto rocks, where it foundered. Local media said the second wave tossed three more people into the water.
Air units from the coast guard and California Air National Guard lifted off after receiving an emergency transmission from a satellite beacon on the Low Speed Chase, as well as a mayday radio call from a nearby yacht, officials said.
The accident came two weeks after a monster wave smashed into an Australian yacht taking part in a round-the-world race. Four crew members were hurt in that accident, which took place 400 nautical miles off the California coast, and the coast guard had to be called in to help. No one was killed.
Shortly after Saturday's accident, helicopter crews quickly used litter baskets and motorized winches to rescue three sailors, said Levi Read, a US coast guard spokesman.
The rescuers also recovered the body of Marc Kasanin (46) of Belvedere, California, who was identified late on Sunday in a release from the San Francisco Yacht Club, where the Low Speed Chase was based.
Mr Read had earlier said the prospects for surviving frigid ocean waters or holding onto the rocky shoals and cliffs of the Farallones depended on the missing sailors' physical fitness, size and clothing.
"The people who were rescued had on cold-weather gear and inflatable life vests," he said.
Ed Lynch, the yacht club's director, said the three rescued sailors were "all pretty shaken up" and taken to San Francisco General Hospital. Two were treated and released on Saturday and one remained hospitalized yesterday with a fractured leg.
"This was an experienced crew who raced together often," Mr Lynch said. "The sailing community is tight-knit, and this is being felt around the world. This is just a terrible tragedy for everyone."
Additional reporting: Reuters/PA