Nine people are presumed dead in the crash of a helicopter that was carrying firefighters over the Shasta-Trinity National Forest, officials said Wednesday.

The crash happened Tuesday night just after the helicopter picked up firefighters, who had been battling a blaze north of Junction City, from a clearing in a remote, rugged region of the forest, said Jennifer Rabuck, spokeswoman for the U.S. Forest Service.

The helicopter was carrying 11 firefighters and two crew members when it went down, according to the Federal Aviation Administration and National Transportation Safety Board. Four people were airlifted to hospitals with severe burns, including two in critical condition, according to the Forest Service.

FAA spokesman Ian Gregor said the Sikorsky S-61N chopper was destroyed by fire after crashing "under unknown circumstances." FAA and NTSB investigators were headed to the scene, about 215 miles northwest of Sacramento.

Firefighters who were waiting to be picked up helped rescue the four injured people after the helicopter crashed around 7:30 p.m. and caught fire, Rabuck said. About three dozen firefighters had to spend the night on the mountain because it became too dark for other helicopters to land, she said.

Nine people — a co-pilot and eight firefighters — were still missing in the wreckage and presumably killed. Recovery efforts have been complicated by the crash site's remote location, and the wreckage is still burning, Rabuck said.

"It's difficult to access," she said. "It's very remote, very steep and heavily forested."

Three of the injured were at the UC Davis Medical Center in Sacramento on Wednesday; two were in critical condition, and one was in serious condition, officials said. The fourth was in Mercy Medical Center in Redding in serious condition.

The firefighters had been working at the north end of a more than 27-square-mile fire burning in the Shasta-Trinity National Forest, part of a larger complex of blazes that total 135 square miles. The complex was about 87 percent contained.

Some of the firefighters, including those in the hospital, were employed by firefighting contractor Grayback Forestry, based in Merlin, Ore.

Mike Wheelock, founder and owner of Grayback Forestry, said he was in Sacramento handling notification of families of his employees. He would not confirm any deaths.

The helicopter was owned and operated by Carson Helicopters Inc., a Pennsylvania company whose firefighting operations are based in Grants Pass, Ore. All 12 of the company's helicopters are being used for firefighting in Oregon and California, said Bob Madden, Carson's director of corporate affairs.

Madden said the helicopter's two co-pilots were Carson employees — one was hospitalized and the other was among the missing. The company would not release their names until officials confirmed their identities and notified family members.

"We are praying for the swift recovery of all the victims, and our hearts go out to their loved ones," Gov. Arnold Schwarzenegger said Wednesday.

Before Tuesday's crash, three firefighters had been killed while on duty in California this year, including one firefighter also assigned to battle the Shasta-Trinity blazes who was killed late last month by a falling tree.

On July 2, a volunteer firefighter in Mendocino County died of heart attack on the fire line. Another firefighter from Washington state was killed July 26 in Siskiyou County when he was burned while scouting a fire.