The US Coast Guard have rescued two injured crew members from a yacht hit by a "monstrous foaming swell" in the Pacific, in an operation made more complicated by bad weather, officials said.

A 29-year-old man and 50-year-old woman were transferred from the 68-foot (21-meter) "Geraldton Western Australia" -- which was taking part in the Clipper Round the World Yacht Race -- onto aCoast Guard cutter, which was expected to arrive in San Franciscoon Monday.

The woman is believed to be British. Other "shaken" crew members -- thought to number 11 others including two with less serious injuries -- remained on board as the yacht limps towards land, said a Coast Guard statement.

"Two injured sailors .. were transferred from their storm damaged yacht to the Coast Guard Cutter "Bertholf" approximately 250 miles offshore today and are now on their way to San Francisco," it said.

The two "are being treated and stabilized by the Cutter Bertholf's medical specialists," it added, after the incident Saturday some 400 miles off the California coast which injured two Britons, an Australian and a Serb national.

In comments posted on the Clipper race's website, South African skipper Juan Coetzer said the boat was hit by a massive wave at dawn Saturday.

"We were racing along in 40-60 knot gusts. The sea was alive with rage. We were making good speed... Then at our watch change, just before the sun came up, a monstrous foaming swell broke over our stern," he said.

The wave smashed the yacht's steering wheel, and left crew "falling all over the boat," it said.

Race organizers had identified the four injured as Britons Jane Hitchens, 50, and Mark Burkes, 47, as well as 62-year-old Australian Max Wilson and Serbian-Croat Nik Brbora, 28, who lives in London.

"The rest of the crew are uninjured but shaken by the incident. All crew next of kin have been informed," they said in a statement. Organizers could not immediately confirm the identity of the two people rescued.

A long-range HC-130 Hercules aircraft was able to drop medical supplies late Saturday, but an attempt to lower rescuers was thwarted because of the weather, and the aircraft had to return to shore.

On Sunday, a Coast Guard cutter was dispatched with a helipad and chopper to link up with the stricken yacht and possibly airlift one or more of the injured, race organizers said.

The helicopter crew had hoped to airlift the injured passengers off, but "once on scene the aviators determined that the boat's rigging and mast presented too great a hazard," said the US Coast Guard statement.

"Instead, one of the Bertholf's two rescue boats, successfully transferred the injured crew to the cutter. Once on board, they were evaluated by the cutter's medical specialists."

Bertholf's commanding officer, "in consultation with medical experts ashore, decided the best course of action was to head back to shore with the injured yacht crew, where the 418-foot cutter is expected to arrive Monday.

The yacht was on the latest leg of the round-the-world race, sailing from Qingdao, China to San Francisco. The next leg should take race participants to New York, via the Panama Canal, the Coast Guard said.