SAN FRANCISCO — Eight firefighters and a pilot are presumed dead in the crash of a helicopter that had just picked up workers battling a blaze in a Northern California forest, officials said yesterday.

The helicopter had lifted off from a clearing in a remote, rugged region of the Shasta-Trinity National Forest, a spokeswoman for the U.S. Forest Service, Jennifer Rabuck, said.

The aircraft was carrying 11 firefighters and two crew members when it went down Tuesday night in the Shasta-Trinity National Forest, according to the Federal Aviation Administration and the National Transportation Safety Board.

Four people were flown to hospitals with severe burns, including two in critical condition, according to the Forest Service.

The Sikorsky S-61N chopper was destroyed by fire after crashing “under unknown circumstances,” an FAA spokesman, Ian Gregor, said. 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 injured after the helicopter crashed around 7:30 p.m. and caught fire, Ms. 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 presumed killed. Recovery efforts have been complicated by the remote location, and the wreckage is still burning, Ms. 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 yesterday; 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.