(CNN) -- Three people are feared dead after a plane crashed and burst into flames in Alaska's Denali National Park, officials said.
The multiengine cargo aircraft crashed into the south-facing slope of Mount Healy, park spokeswoman Kris Fister said Sunday. Fister said it appeared that the three people reported onboard did not survive.
The Fairchild C-123 plane's crash sparked a one-acre blaze that firefighters were still working to extinguish hours later, she said.
The plane was registered to All West Freight Inc. of Delta Junction, Alaska, she said.
National Transportation Safety Board investigators are scheduled to arrive on the scene Monday morning.
Initial reports indicate the plane crashed around 4:15 p.m. (8:15 p.m. ET), FAA spokesman Allen Kenitzer said.
Jeff Kowalczyk said he was hiking through the park with his wife when he looked up and saw the plane almost upside down as it crashed into the hillside a few hundred yards away.
Kowalczyk, an EMT, said he and his wife, a nurse, rushed to the scene after seeing the cargo plane's plunge. But the crash set the aircraft ablaze, he said, preventing them from getting close.
"The whole experience was really surreal," he said.
CNN's Chuck Johnston and Leslie Tripp contributed to this report.