– A tornado severely damaged about 15 trailers housing workers in North Dakota's oil patch on Monday, the National Weather Service said.

It wasn't immediately clear if anyone was injured when the twister struck the camp about 5 miles south of Watford City, which is in the western part of the state about 30 miles southeast of the oil boom hub city of Williston.

People who answered the phone at the McKenzie County Sheriff's Office and McKenzie County Hospital in Watford City declined to discuss the matter.

Although the tornado threat for the area had passed, McKenzie County emergency management officials were asking people to stay off the roads because emergency vehicles were having a difficult time reaching the scene.

The oil boom has led to a population explosion in western North Dakota, bringing in tens of thousands of people looking for work. Many reside in hastily-assembled trailer parks or man camps, which contain prefabricated structures that can resemble military barracks.

A man who photographed the tornado said the twister remained on the ground for nearly a minute.

William Bunkel told the Associated Press late Monday that he was in Watford City with some co-workers when the tornado warning came.

He says they saw the funnel cloud form several miles to the south and watched it touch down and remain on the ground for nearly a minute before retreating into the sky and disappearing.

Associated Press