FORT CHAFFEE, ARK., JULY 28 -- An Army helicopter crashed into a hillside on a night flight in the early stages of a war game, killing five soldiers and injuring eight others, authorities said today.

Rescuers had to walk more than a mile to find the UH-60 Blackhawk helicopter about five miles south of Charleston and used other helicopters to get the injured to St.

Edward Mercy Medical Center at Fort Smith, said Fort Chaffee spokesman Cecil Green.

It was one of two fatal military helicopter crashes Friday night. The second, in the Southern California desert, killed two Marines and injured three others.

Green said he did not know if there was any indication that the helicopter at Fort Chaffee had problems before it crashed in

a hilly region north of the Ouachita Mountains. He said weather was not a factor.

"The only thing we know is that the helicopter was in radio contact with one of the team members on the ground," he said. The ground unit notified headquarters of the crash, he added.

Reporters were not allowed at the crash site.

The men aboard the $4.6 million helicopter were participating in an early stage of an exercise slated to involve about 3,000 soldiers at its peak next week. About 300 soldiers were participating in the early stages, Green said.

"Realism is the key, and it's played out basically in the field for about a 10-day war when it starts," he said.

He would not say where the helicopter normally was based.

In Southern California, a UH-1N Huey helicopter crashed in the Chocolate Mountain Bombing Range, about 55 miles northwest of the Marine Corps Air Station at Yuma, Ariz., said Marine Lance Cpl. Lisa Rodriguez.

The Huey was carrying practice rockets and small-caliber ammunition. It was assigned to the Medium Light Attack Helicopter Squadron 367, 3rd Marine Aircraft Wing, at Camp Pendleton, Rodriguez said.

Names of the victims were withheld until relatives could be notified.