YOSEMITE NATIONAL PARK, Calif. (AP) — An air tanker fighting a wildfire near Yosemite National Park in Northern California crashed Tuesday, but there was no immediate word on the condition of the pilot, who was the only person aboard, officials said.

The plane went down at about 4:30 p.m. within a mile of the park's west entrance, Yosemite spokesman Scott Gediman said. Rescue crews were working their way through difficult terrain to reach the plane.

"It's very rugged terrain," said Janet Upton, a spokeswoman for the California Department of Forestry and Fire Protection. "We determined there was a crash, but they're still trying to work their way through pretty rugged terrain to determine the status of the pilot. Obviously we're hoping for the best, but the situation is very serious."

The airplane, manufactured in 2001, is an S-2T air tanker, which is flown by a single pilot and has no other crew members. The tanker uses twin turbine engines and is capable of carrying 1,200 gallons of fire retardant, said another CalFire spokesman, Daniel Berlant.

A California Highway Patrol spokesman, Officer Steven Lewis, said CHP Sgt. Chris Michael witnessed the crash as he was helping to close state Route 140 where it enters the park.

"All the tourists and residents were being turned away," Lewis said, when Michael reported that he had just witnessed "a bomber collide into the river canyon, the canyon wall, and watched it explode in flames and reported there was plane debris landing in the highway."