A Union Pacific freight train has crashed into the back of another freight train in Wyoming, killing at least one crew member with another missing and derailing more than 50 train cars.

Lt Don Hollingshead of the Laramie County Sheriff’s Office says the crash was reported at around 7:45pm on Thursday in a sparsely populated area about 18 miles west of Cheyenne.

Union Pacific spokeswoman Raquel Espinoza said on Friday that 56 rail cars derailed, but no hazardous materials were released.

Ms Espinoza says both eastbound trains were hauling mixed freight, but one was stopped.

Contrary to earlier reports, Ms Espinoza says no other crew members were injured. She says the crew of the stopped train had departed their locomotive before the crash.

The National Transportation Safety Board is investigating.