SAN FRANCISCO — As many as nine people were 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, which is east of Eureka, 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 — three firefighters and one of the two pilots — were airlifted to hospitals with severe burns, according to the Forest Service.

Ten of the firefighters, including the three in the hospital, were employed by Oregon firefighting contractor Grayback Forestry, according to Kelli Matthews, a spokesman for the Merlin-based company. Grayback’s tally showed that seven of its employees were unaccounted for late Wednesday, and the company does not know whether any firefighters from any other companies or government agencies also were on board, Matthews said.

She said the company was in the process of notifying families of the missing firefighters as well as fielding calls from anxious relatives asking whether their family members were among the injured or dead.

FAA spokesman Ian Gregor said the Sikorsky S-61N chopper was destroyed by fire after crashing “under unknown circumstances.” The NTSB, which is leading the investigation, was headed to the scene, about 215 miles northwest of Sacramento, while the Trinity County Sheriff’s Department was leading the search for crash victims.

Firefighters who were waiting to be picked up helped rescue the four injured people after the helicopter crashed around 7:45 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.

Federal authorities 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 ongoing wildfire in the forest, Rabuck said.

“It’s difficult to access,” she said. “It’s very remote, very steep and heavily forested.”

The firefighters had been working at the north end of fire that has burned more than 27 square miles in Shasta-Trinity National Forest since June 21, part of a larger complex of blazes that total 135 square miles. The complex was about 87 percent contained.

“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.

Mike Wheelock, Grayback’s founder and owner, said the company had two 20-person crews working the fire, a mix of young seasonal firefighters and professionals.

“We are just right now concentrating on all the families and our employees,” Wheelock said while visiting UC Davis Medical Center in Sacramento, where two of his injured employees were being treated. “We are very concerned about them because we are very tight-knit.”

Grayback firefighters Michael Brown, 20, and Jonathan Frohreich, 18, as well as one of the two pilots, were being treated at the UC Davis hospital, according to the contractor. Brown was upgraded to fair condition late Wednesday and Frohreich remained in critical condition, according to the hospital and fire officials.

A medical center spokesman said the hospital also was treating a crash victim in critical condition named William Coultas, but could not confirm whether the patient was the helicopter’s co-pilot.

Leora Frohreich, Jonathan Frohreich’s grandmother, said this was the young man’s first working as a wildland firefighter and that the experience had persuaded him to further his education. He planned to attend a mechanics school this fall. He had worked on a fire near the southern Oregon town of Williams for three weeks and then was on the Shasta-Trinity fire for four days, the grandmother said. His crew was being flown out for some rest when the helicopter crashed, she said.

“I’m so thankful because he’s just lucky to be alive,” Frohreich said, adding that the firefighter’s parents, sister and girlfriend had gone to Sacramento to be with him. “You can’t be in a crash like that and not hurt.”

Another Grayback employee, identified as Richard Schroeder, 42, was in serious but stable condition at Mercy Medical Center in Redding, officials said.

The helicopter was owned and operated by Carson Helicopters Inc., a Pennsylvania company whose firefighting operations are based in Grants Pass.

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.

The Forest Service and the sheriff’s department would not disclose Wednesday whether they had recovered the bodies of any victims from the crash site or what was involved in the search effort. The Trinity County coroner’s office said it did not have any information to release.

Before Tuesday’s helicopter crash, three firefighters were 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.

Meanwhile, fire crews were busy containing a series of small fires sparked by an electrical storm that generated an estimated 2,000 lightning strikes in northern California, southern Oregon and western Nevada on Tuesday and Wednesday, said Basil Newmerzhycky, a Forest Service meteorologist in Redding.

The lightning storm set off at least a “few dozen” small fires across the region, none of which had grown into major blazes so far, Newmerzhycky said. By contrast, a massive lightning storm on June 21 generated about 8,000 strikes that sparked more 2,000 fires that became the largest fire event in California history.

The storm stoked a complex of blazes in rural Butte County more than doubled in size to 4 square miles on Tuesday after firefighters were forced to briefly retreat from unpredictable winds unleashed by passing thunderclouds, state fire officials said. That fire was about 50 percent contained and threatened about 75 homes Wednesday.

A wildfire outside Yosemite National Park that was started July 25 by a person taking target shooting practice was completely contained by Wednesday morning, after destroying 30 homes and consuming about 53 square miles in Mariposa County. Officials revised their count of homes destroyed again — up from 28 — after surveying the damage.

Schwarzenegger also declared a state of emergency in Humboldt County on Wednesday because of the unhealthy air quality caused by fires there. It’s one of 13 county emergency declarations the governor has declared this year due to the blazes.

— Associated Press writer Don Thompson in Sacramento and Jeff Barnard in Grants Pass also contributed to this report.