Officials in California were searching Friday for survivors of a midair collision between a Coast Guard plane and a Marine Corps helicopter — but the nine people on board the two aircraft were feared dead.

Investigators are trying to determine why the plane, on a nighttime search for a boater, collided with one of four Marine Corps helicopters flying in formation to a military training island off Southern Calfornia.

Federal Aviation Administration spokesman Ian Gregor said the Thursday night collision occurred minutes after control of the Coast Guard C-130 was handed off from FAA controllers to military air controllers.

All seven people aboard the Coast Guard plane and the two-person crew of the Marine Corps AH-1W Super Cobra helicopter remain missing Friday. The search is focused on a debris field 50 miles off the San Diego coast.

Pentagon spokesman Bryan Whitman says that although the search continues, the collision likely killed the nine crew members.

Petty Officer Henry Dunphy told reporters Friday morning that they were still in an active search-and-rescue phase.

"Our assumption is always that they are alive," Dunphy said. "We have not found any human remains at this point. There is a substantial debris field."

Coast Guard Rear Adm. Joseph Castillo echoed those sentiments Friday afternoon.

"We'll continue to search with the hopes of finding survivors," he said.

Some of the crash debris has been recovered from the water and is being analyzed, Castillo said.

The collision was reported at 7:10 p.m. Thursday, about 50 miles off the San Diego County coast and 15 miles east of San Clemente Island, Coast Guard spokeswoman Petty Officer Allyson Conroy said.

A pilot reported seeing a fireball near where the aircraft collided, Gregor said, and the Coast Guard informed the FAA that debris from a C-130 had been spotted.

The Coast Guard crew members had survival gear onboard their aircraft, including exposure suits that could have allowed them to survive in the water for hours, Dunphy said Friday.

At least seven Coast Guard and Navy ships and several helicopters continued a search that ran overnight under a bright moon in calm seas.

"We've pretty much thrown everything we have at it right now," Dunphy said.

The Coast Guard plane was based in Sacramento and was on a search-and-rescue mission when the collision occurred, Dunphy said.

The AH-1W Super Cobra helicopter was on a training mission when it went down, said Cpl. Michael Stevens, a spokesman for the Miramar Marine Corps Air Station.

The Cobra and its crew are part of Marine Aircraft Group 39, based at Camp Pendleton, and the 3rd Marine Aircraft Wing, which is headquartered at Miramar, Stevens said.

San Clemente Island is the southernmost of the eight Channel Islands located 68 nautical miles west of San Diego. The Navy has owned and trained at San Clemente Island since 1934, according to the island's Web site. Naval Air Station, North Island is responsible for the island's administration.

Meanwhile, the Coast Guard resumed its search Friday morning for two missing Navy pilots and their plane off the central Texas coast. The search had to be suspended Thursday night because of stormy weather.

Petty Officer Charles Reaves said a plane and a helicopter resumed the search shortly after 7:30 a.m. Friday.

Naval Air Station Corpus Christi lost contact with the Navy T-34 training plane Wednesday afternoon. The single-engine plane's last known location was near San Jose Island, east of Rockport and 2 miles offshore in the Gulf of Mexico.

Additional coverage from Fox 5 San Diego

More at MyFoxLA.com.

The Associated Press contributed to this report.