LOS ANGELES, (AFP) - A small plane crashed in the northern state of Montana, killing all 17 people on board, many of them children heading on a skiing holiday, federal aviation officials said.

"We think that it was probably a ski trip for the kids," Federal Aviation Administration spokesman Mike Fergus told AFP, adding that preliminary reports showed 17 people were killed when the plane plunged into a cemetery.

The plane, a single engine turboprop, was heading from Oroville, California, just north of San Francisco on a 900-mile (1,500-kilometer) journey to Bozeman, Montana.

Fergus said the crash occurred at around 2:30 pm (4.30 am Singapore time), just south of the Bert Mooney Airport in Butte, about 80 miles (130 kilometers) west of Bozeman.

He said the plane "crashed into Holy Cross cemetery, about 500 feet (150 meters) from the airport while attempting to land."

Neither spokesman speculated on the cause of the crash or on weather conditions prevalent at the accident site.

Dorr said a team of investigators from the National Transportation Safety Board was heading to the area.

"We watched this plane just take a nose-dive right into the cemetery," a witness Martha Guidoni told CNN. A picture she snapped of the accident scene showed towering flames shooting up behind a cemetery and one of a series of towering trees ablaze.

She and her husband Steve rushed to the scene of the crash to see if anybody could be helped, but she said: "We were too late. There was nothing to help."

Steve Guidoni said when he got to the crash site "everything was on fire.

"And there wasn't much left of the plane, actually. It was embedded in the ground. It went into the ground. It caught a big tree on fire.

"I looked to see if there was anybody I could pull out, but there wasn't nothing there. I couldn't see nothing. Some luggage strewn around and fire. That was about it. There was some plane parts."

He said the plane left a hole 20 feet (six meters) deep in the ground.

Dorr said the plane was apparently owned by Eagle Cap Leasing from Enterprise, Oregon. He said it normally carries nine or 10 people, but that the fatal flight might have been configured to legally carry more passengers.

Aviation attorney Mary Schiavo, a former federal inspector, told CNN she was familiar with the type of aircraft and said it was not certified to carry such a large load.

"This aircraft is only certified for nine passengers. Granted, they said that they were children, but unless people were holding them in their laps, which is not a safe way to fly, only nine passengers and two crew," Schiavo said.

"The maximum weight when you're landing this plane, you're only allowed to have 9,000 pounds (4,000 kilograms) on it and the empty weight is almost 6,000 pounds (2,700 kilograms). So, that's not a lot of leeway."