Emergency personnel responded to an explosion at an oil field salt water disposal site southeast of Watford City on Thursday.
Karolin Jappe, McKenzie County's emergency manager, said there was one man on site at the time of the incident. The man was not injured.
The incident, which took place at a White Owl Energy Services site, was reported at 12:15 p.m.
Jappe said the cause of the explosion and fire is unknown.
"It's unusual to have (fires) at a salt water disposal in the winter," she said. "Usually it's in the summer when lightning hits it. We can have four to five per summer."
Jappe said the fire at the site will be allowed to burn out on its own. In cases where no other structures or people are in danger, she said it is usually better to let them burn.
She said putting out the fire can cause larger problems with the salt water spreading and contaminating the ground, which is extremely costly to remedy.
The incident has been reported to the North Dakota Department of Health, Jappe said.
Watford City police public information officer Sgt. Jeffrey Jensen said the McKenzie County Sheriff's Department is investigating the cause of the explosion.