Two Air Force helicopters crashed early Friday during a training mission over Nevada, and the fate of the 12 people on board was unknown.

The HH60G Pave Hawk helicopters, part of a rescue squadron based at Nellis Air Force Base, were on a night mission when they crashed about 1 a.m. PDT. The wreckage of the helicopters was found about an hour later.Gen. Theodore Lay, commander of the 57th Wing at Nellis, said families of crew members were being contacted. Authorities gave no information on whether anyone survived.

Maj. Byron James, an Air Force spokesman at the Pentagon, said the two helicopters apparently collided. But Lay said he was not sure whether it was a collision or whether the two helicopters both crashed into the rugged mountainous terrain in which they were operating.

The crash site is 25 miles north of Indian Springs, Nev., a remote auxiliary Nellis air field 33 miles northwest of Las Vegas.

The bombing and gunnery range covers 5,200 square miles, and is a highly restricted area. It is the site of some of the world's most sophisticated aerial exercises, including Red Flag aerial war games that draw pilots from around the world.

Nellis spokesman Mike Estrada said the terrain where the helicopters crashed is some of the most difficult on the sprawling range.

"Our folks had a pretty difficult time getting up to the crash site," Estrada said.

A team of search and rescue and emergency forces from the Air Force, Bureau of Land Management and Department of Energy were working with local authorities.

The Air Force owns only 10 of the $12 million Pave Hawk helicopters of the type that crashed today. They normally carry a crew of four people - two pilots, a flight engineer and a gunner. They are built by Sikorsky Aircraft Corp.

The Nellis helicopters are part of the 66th Rescue Squadron, the largest rescue squadron in the Air Force. Units just recently returned from duty in Turkey and Southeast Asia.