UPDATE: Officials are urging evacuation of the area surrounding the derailment.

With increasing amounts of crude oil being shipped by train, we're seeing more of these hazardous explosions:

A train carrying crude oil from North Dakota's oil patch derailed Monday near the small town of Casselton, setting off a series of fiery explosions. No injuries were initially reported, but officials were warning residents to stay indoors as the situation unfolded.

BNSF Railway spokeswoman Amy McBeth said a train carrying grain was first to derail, and it knocked several cars of the mile-long oil train off adjoining tracks. Several explosions were reported, she said.

Cass County Sheriff's Capt. Mitch Burris also told The Associated Press that the derailment appeared to result from the crude oil train striking a grain car, but he said investigators were still trying to determine exactly what happened.

Cass County Emergency Manager Dave Rogness said the town's 2,400 residents were told to stay indoors as a precaution.

Rogness said crews were calling for truckloads of sand to help contain leaking material. He says the derailment occurred near the city's ethanol plant.

Terry Johnson, the manager of a grain dealer less than a mile from the derailment, said he had heard at least six explosions in the two hours following the incident.

"Each one, you could hear the explosion," he said. "It shook our building and there was a huge fireball."

Johnson said he was staying inside his grain business, as directed by authorities, but could see the disaster through a window.

"The town is covered with black smoke," he said. "The wind is blowing a little, so the town doesn't have to breathe it."

State health officials were in Casselton and plan to check for health hazards once the fires are out, said Dave Glatt, director of the Health Department's environmental health section.