U.S. aviation officials are investigating the crash of a single-engine plane that plunged into a cemetery in the northwestern state of Montana, killing all 14 people on board.

The Federal Aviation Administration says seven children were among the dead.

Authorities say they believe the passengers were on their way to a ski trip Sunday.

The plane took off from southern California, and made other stops in California before heading north to Bozeman, Montana.  Authorities say the pilot changed course 140 kilometers short of its final destination and crashed in Butte, Montana.

Witnesses say the Pilatus turbo-prop aircraft burst into flames when it crashed into a cemetery.

The cause of the crash is not known.

Some information for this report was provided by AP.