UPDATE 10 a.m. Friday: Union Pacific Railroad spokeswoman Raquel Espinoza says that as of 10 a.m. Friday the search for the Union Pacific crew member reported missing after last night's train crash is ongoing. One UP employee was killed in the crash. She also said investigators have learned the two crew members in the parked train which was hit from behind had exited the train prior to the collision

UPDATE 9:45 a.m. Friday:  A news release from the Wyoming Department of Transportation [WYDOT] says the accident is being investigated by the Union Pacific Railroad safety team. Following the investigation, it could take up to 10 days from today to clean up the crash scene, according to the release.

While the cleanup continues the I-80 service road will be closed to traffic at exit 342. Traffic accessing quarries in the area will be allowed. A truck parking area at Exit 345 is also closed.

UPDATE: Cheyenne Mayor Marian Orr has released a statement on the deadly train crash in western Laramie County Thursday evening that claimed one life and has left another person missing.

“This was a significant and tragic event. We are a community of railroaders and tonight our community has experienced loss. And if you pray, please pray.” said Orr.

Responding agencies included Cheyenne Fire Rescue, F.E. Warren, Laramie County Sherriff’s Office, American Medical Response (AMR), Laramie County Fire District No. 1, Laramie County Fire District No. 2, Laramie County Fire District No. 10, Cheyenne/Laramie County Health Department, and Wyoming Highway Patrol.

As of 5:30 a.m. Friday, the search for a Union Pacific employee reported missing in the crash was continuing. Officials have so far not released the names of any of the people involved

UPDATE: According to Lt. Don Hollingshead of the Laramie County Sheriff's Department, the derailment was reported around 7:45 p.m. and involved two eastbound Union Pacific trains, one of which is believed to have rear-ended the other. The crash occurred about 18 miles west of Cheyenne.

Hollingshead says four UP employees were in the crash, one of whom is reported to have been killed. One other person is missing and the other two were not  seriously injured. The person who died and the missing person are believed to have been in the engine of the train which struck the other from behind. No evacuations have been ordered. The cargo on the trains was reportedly "mixed."

In addition to the sheriff's office, the Wyoming Highway Patrol, Union Pacific officials and other emergency responders are on the scene

Original Story: Details are still sketchy, but according to a spokesman for the Laramie County Sheriff's Department, at least one person has been killed in a derailment of a Union Pacific train in western Laramie County on Thursday evening.

That's according to Lt. Don Hollingshead with the Sheriff's Department.

The derailment is believed to have happened near Harriman Road. Townsquare Media's Joy Greenwald is headed to the accident scene. Attempts to contact Union Pacific officials this evening have so far been unsuccessful.

Meanwhile, the Wyoming Department of Transportation says the Warren Interchange truck parking lot exit between Cheyenne and Buford is closed due to the derailment.

We will report further details as they become available.