Military helicopters and ships scoured the waters off San Diego on Friday for nine people involved in a midair collision between a Coast Guard plane and a Marine Corps helicopter.
After searching most of the day, rescue teams did not find any survivors or bodies, only a field of debris floating in the Pacific. Military officials said they did not know how the crash had occurred, or which aircraft had struck the other, saying they were focused on search efforts.
Seven people were aboard the Coast Guard’s C-130 transport plane and two were in the Marine Corps’ AH-1 Cobra helicopter when the crash occurred Thursday at 7:10 p.m., officials said. They were flying 15 to 25 miles east of San Clemente Island, a narrow strip of land off the Southern California coast used by the Navy for training exercises.
Right before the crash, air traffic controllers with the Federal Aviation Administration told the Coast Guard pilot “to contact military air traffic controllers,” said Ian Gregor, an F.A.A. spokesman.
The F.A.A. then ended communication with the pilot “several minutes before the accident occurred,” Mr. Gregor said, adding that he did not know if the pilot contacted the military air traffic controllers.
F.A.A. controllers, he said, did not talk to the helicopter pilot.
By noon Friday, rescue teams had expanded the search area to a 24-by-28-mile stretch of sea roughly 50 miles off the coast of San Diego to accommodate mild winds and shifting currents, said Officer Henry Dunphy, a Coast Guard spokesman.
The Coast Guard searched for people after one of its planes collided with a Marines helicopter.
“They’re throwing everything they can into that search,” he said.
Officials had notified all family members of the missing, Mr. Dunphy said, but would not release names while the search continued.
“There is about a 19-to-20-hour survivability time that someone could have in the water,” Mr. Dunphy said.
At a noon news conference in San Diego, Rear Adm. Joseph Castillo of the Coast Guard said: “Our people are very highly trained in survival techniques. They are very highly fit, physically fit. They are able to survive things that you would be surprised at."
Three Coast Guard ships and an MH-60 Jayhawk helicopter were joined by four Navy vessels and several helicopters in the search Thursday night. Those teams continued combing the waters Friday afternoon, Admiral Castillo said, and waited for crews from Los Angeles and Oregon to relieve them.
The Coast Guard plane had been dispatched from Sacramento, the closest C-130 unit, to look for a man in a 12-foot dinghy that had been reported as missing. Mr. Dunphy did not have any additional details on the original rescue mission; the man was still missing Friday afternoon.
The Marine helicopter was one of four that had left Camp Pendleton Thursday night to escort two heavy-lift CH-53E troop transport helicopters carrying Marines to San Clement Island for training exercises, said Lt. Greg Wolf, a Marine spokesman.
“They were out there on a routine training,” Lieutenant Wolf said. “The ones not involved in the crash returned safely to Camp Pendleton.”
A pilot in the area reported seeing a fireball in the area near the crash, said Mr. Gregor with the F.A.A.
Lieutenant Wolf said the Marines in Southern California had halted all air operations while the search continued.
Meanwhile, in Texas, Coast Guard teams resumed their search for two Navy pilots whose plane disappeared Wednesday during a training mission near Corpus Christi. Naval fight controllers lost contact with the plane at about 3:20 p.m. Wednesday, and were combing a search area of 4,500 square miles.