DENVER -- Thirty-four cars of a Union Pacific train derailed about 8 miles west of Limon, officials said Thursday afternoon.

The eastbound train was hauling coal at the time, said Mark Davis, spokesman for Union Pacific.

Davis said it was too early to guess why the train derailed. He said managers from Union Pacific will need time to upright the train and determine the cause of the derailment.

Davis said it was "very fortunate" that no one was injured.

The train derailed in a rural area away from homes and businesses.

Heavy equipment is en route to begin cleaning up the mess, Davis said.

Davis says crews would work through the night to remove derailed cars and repair the track. He says the line may reopen Friday.

It wasn't immediately known where the train originated.

The line where the accident happened carries traffic from Denver to Kansas City. Davis says a detour is available through Cheyenne, Wyo., and Nebraska.