Story highlights Sheriff urges residents to leave town because winds are expected to shift

Fire will take 12 hours to burn itself out

Officials aren't sure if one train derailed before the accident

Smoke can be seen in Fargo, 25 miles away

A wreck involving two trains, one of which was carrying crude oil, sparked a large fire Monday that sent huge flames and dangerous smoke into the sky, North Dakota authorities said.

There were no reports of injuries from the accident, said Sgt. Tara Morris with the Cass County Sheriff's Office, but "with the oil on fire there are hazardous conditions, and we are directing all people in the area to shelter in-place and stay indoors."

Firefighters will be forced to let the fire burn out, which may take as long as 12 hours from the time of the accident (2:12 p.m. CT), because they cannot get close enough to the flames, she told CNN.

The incident occurred one mile west of Casselton, a town of 2,300 residents about 25 miles west of Fargo. Huge plumes of smoke could be seen in Fargo, Morris said.

The sheriff's office advised all residents in Casselton and two nearby townships to evacuate because the winds were shifting due to a high-pressure system.

A Red Cross shelter in Fargo was available, the sheriff's office said.

Morris said it was unclear how the accident happened and authorities are trying to determine whether one of the trains derailed before they collided.

About 10 of the cars on the train carrying oil were fully engulfed in flames. At least a dozen firefighters are involved, she said.

An official with the Federal Railroad Administration said it will support a National Transportation Safety Board investigation of the accident.