An explosion in the Jonah gas field has injured five workers, one of them critically.

Encana officials say the cause isn't known, but contract workers were welding at the time.

Five of six gas condensate tanks exploded at the well site around 10:20 a.m. Friday.

The Sublette County Sheriff's Office says the worker in critical condition was taken to a hospital in Salt Lake City.

Another worker in serious condition was taken to Idaho Falls, Idaho.

Two other workers were taken to Rock Springs and Salt Lake City in what doctors described as stable condition.

Another worker was treated in Pinedale and released.

Encana officials say federal safety investigators will be on site this weekend.

The Jonah field 35 miles south of Pinedale is the seventh-biggest U.S. gas field.

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