Updated

Officials in North Dakota said early Tuesday that nine people were injured, one critically, when a tornado struck an oil worker camp.

McKenzie County Emergency Management Director Jerry Samuelson said the tornado that struck the camp 6 miles south of Watford City on Monday destroyed eight trailers where workers lived. Samuelson said the person who was critically injured was taken to a hospital in Minot, N.D. for treatment, while the other eight injured were treated and released.

Samuelson says rescue crews are searching a large amount of debris, but he's confident no one is missing. Hesays the camp where the tornado hit had quite a few more trailers just a few days ago, so the casualties could have been higher had it happened earlier.

Watford City is located in western North Dakota, about 30 miles southeast of the oil boom hub city of Williston.

William Bunkel, who works for a trucking company, told The Associated Press late Monday that he was in Watford City with some co-workers when the tornado warning came. They had just moved their vehicles inside because of large hail when they spotted the funnel cloud.

"We saw it form, come out of the sky, hit the ground and go back up into the clouds," he said.

Bunkel, 38, took photos of the twister and estimated that it remained on the ground for nearly a minute. He said he couldn't see any debris.

"It was a little bit too far away. We just saw the clouds and the rotation," he said.

Samuelson said that there had been three reported sightings of funnel clouds, part of a storm that produced baseball-sized hail.

The oil boom has fueled a population boom for the area, bringing in tens of thousands of people looking for work. Many live in hastily-assembled trailer parks or man camps, which contain pre-fabricated structures that can resemble military barracks. Some companies rent blocks of hotel rooms for employees to live in, and some workers sleep in their cars or even tents.

Housing developments are constantly popping up in big areas of town that didn't exist on maps a couple of years ago. But they are still not enough to keep pace with demand and oil money has pushed rents to among the highest in the nation: A simple one bedroom apartment in Williston can easily cost $2,000 per month in rent. Even a spot to park a trailer can cost over $800 per month.

The Associated Press contributed to this report.