North Dakota Tornado
The tornado struck an oil worker camp in North Dakota   YouTube

Nine people have been injured by a tornado which ripped through an oil worker camp in North Dakota.

One of the victims of the twister which hit the camp five miles south of Watford City was in critical condition, according to emergency officials.

"Obviously, we're very fortunate there are no deaths, to our knowledge," McKenzie County Emergency Management Director Jerry Samuelson said.

Samuelson added that emergency crews had searched the debris at the campsite but were confident nobody was missing.

The nine people injured were all in their trailers when the tornado struck with no time to take shelter due to the speed of its onset.

"We saw it form, come out of the sky, hit the ground and go back up into the clouds," said eyewitness William Bunkel, a truck company worker.

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

The storm produced large hail, heavy rain and high winds, according to Adam Jones, a meteorologist with the National Weather Service.

North Dakota is witnessing an oil boom which has attracted tens of thousands of people looking for work, many who live in trailer parks.