Speculation on why a plane crashed in Montana on Sunday, killing 14 people, has shifted from overcrowding to ice on the wings.

Seven children and seven adults died in the crash.

Safety experts said icing conditions Sunday were similar to those existing when a Continental Airlines turboprop plane crashed into a home outside Buffalo, killing 50.

The single-engine Pilatus PC12 was designed to carry 10 people, but overcrowding seems to be less likely to be a cause of the crash as half of those on board were small children.

Relatives gave the children's ages as 1, 3, 5, 7, and 9, plus two 4-year-olds.

They were heading to an exclusive high-end ski resort, where Bill Gates and former U.S. vice-president Dan Quayle are members.

The single engine turbo-prop plane crashed just 150 metres from the runway at Bert Mooney Airport when it went down in Holy Cross cemetery on Sunday afternoon.

Witnesses reported seeing the plane swerve dramatically to the left, causing some to think the low-flying plane was performing aerial stunts.

"He jerked the plane to the left too quickly and lost control of it, but that's just my guess," 14-year-old Kenny Gulick told CBS.

"And all of a sudden it went into a nosedive. I noticed the pilot trying to pull up but he was extremely low to the ground and he didn't pull up in time."

Dave Griffiths, of KFBB TV, told CTV's Canada AM that other witnesses also reported seeing the plane veering around in the sky, before smashing into the ground.

"The cemetery is right next to the airport, and first-hand witnesses thought they saw the plane taking a bunch of deep turns and wide turns and all of a sudden nose diving right into the ground," he said.

Griffiths, who was one of the the first reporters on the scene, spoke to local witnesses who described hearing a loud crash, followed by an explosion or a column of fire that shot into the sky.

Death toll confirmed

Investigators from the National Transportation Safety Board were on the scene early Monday, attempting to piece together what happened in the final minutes.

Complicating their job is the absence of "black box" devices. Planes that small do not need to carry flight data or cockpit recorders according to safety regulations.

Karen Byrd, an operations officer with the U.S. Federal Aviation Authority, confirmed the death toll on Monday morning.

The passengers were believed to have been en route to a ski trip in Montana, from Oroville, Calif., though that has not been officially confirmed.

At one point the pilot suddenly changed the flight destination from Bozeman, Mt., to nearby Butte.

Early reports put the death toll at 17.

Flight plan changed en route

The aircraft had departed from Oroville, Calif., and the pilot had filed a flight plan showing a destination of Bozeman, about 135 kilometres southeast of Butte. But the pilot cancelled his flight plan at some point and headed for Butte, Fergus said.

It was partly cloudy, the visibility was 16 kilometres and winds were blowing from the northwest around 16 km/h at the time of the crash, according to hourly temperature information from the National Weather Service.

In Oroville, Calif., where the plane took off, Tom Hagler said he saw a group of children and four adults Sunday morning at the Oroville Municipal Airport, about 110 kilometres north of Sacramento.

Hagler, owner of Table Mountain Aviation, said he let the children into his building to use the restroom.

"There were a lot of kids in the group," he said. "A lot of really cute kids."

The crash is the fourth major plane accident in the U.S. in slightly more than three months.

With files from The Associated Press