Officials with Amtrak say the eastbound train derailed at approximately 10 p.m. at a railroad crossing near Weld County Road 63 and Weld County Road 398.
Amtrak said there were 69 passengers on board.
The Colorado State Patrol said a train engineer, a 42-year-old male from Utah, suffered life-threatening injuries, according to CBS News.
It is unclear why the semi was on the tracks or what happened leading up to the crash.
MP/PR