The U.S. Coast Guard and Navy are searching for survivors from a collision between a C-130 plane carrying seven people and a Marine Corps helicopter carrying two others.

The mid-air crash was reported at 7:10 p.m. local time on Thursday, said Coast Guard spokesperson Petty Officer Allyson Conroy.

The approximate location of the collision was about 80 kilometres off the San Diego Count coast and about 24 kilometres east of San Clemente Island, Conroy said.

An all-night search took place under moonlight on a calm evening, Coast Guard Petty Officer Henry Dunphy said Friday morning, as the search continued.

Dunphy said the people on board the Coast Guard airplane had access to survival gear, including exposure suits that could allow them to survive in the water for hours.

"We're hoping to find survivors," Dunphy said. "We're not ruling that out."

Dunphy said the C-130 plane was based out of Sacramento, Calif., and involved in a search-and-rescue mission at the time of the crash.

The AH-1W Super Cobra helicopter was on a training mission when it crashed, said Miramar Marine Corps Air Station spokesperson Cpl. Michael Stevens. It was based at Camp Pendleton and the 3rd Marine Aircraft Wing, which is headquartered in Miramar,

Calif. The FAA said the chopper was carrying two people.

San Clemente Island has been owned by the Navy since 1934 and is located 125 kilometres west of San Diego.

With files from The Associated Press