An old field camp was hit by a tornado on Monday night in North Dakota, injuring nine people and destroying at least 12 recreational vehicles, said officials.

The tornado hit about six miles south of Watford City. Eight people had minor injuries; one person was flown to Trinity Hospital in Minot, the McKenzie County Sheriff's Office said.

The others were treated and released.

Rescue crews are searching between the debris, but they don't believe anyone is missing. Jerry Samuelson, the McKenzie County Emergency Management Director, said that if the tornado had hit a few days earlier, it could have been worse. There were more trailers a few days ago.

William Bunkel told the Associated Press that he and co-workers heard the tornado warning after they had moved their vehicles inside because of large hail. That's when they saw the funnel cloud.

"We saw it form, come out of the sky, hit the ground and go back up into the clouds," he said. "It was a little bit too far away. We just saw the clouds and the rotation."

Bunkel took pictures of the twister and he believed it was on the ground for about a minute.

The area has seen a boom in population because of oil. Tens of thousands of people have come to look for jobs, some of which were living in trailer parks or man camps. Some companies rented hotel rooms for their employees, but some had to sleep in their cars.

More housing developments are being built, and there are big areas in the town that didn't have houses on them just a few years ago. The apartments have not been able to keep up with demand, which means rent has been hiked up. A one-room apartment in Williston can cost $2,000 per month, and a spot at the trailer park can cost about $800 a month.