Firefighters were allowing a massive fire at the Red River Oilfield Service Co.’s facilities in the Williston Basin to burn late Tuesday as North Dakota state health officials monitored the situation.

A cause had not been identified for the blaze, which began around midnight Monday in an industrial part of the town of Williston, in the northwest corner of the state. Williston is in Williams County, which accounts for roughly 15% of total North Dakota crude oil production.

Reports from the scene indicated there were no injuries and no immediate threat to public health or safety from the blaze. A state air monitoring site in Williston is maintained by the North Dakota Department of Health, and other agencies were on the scene with portable air quality monitoring equipment.

State health officials said smoke from the fires could “adversely affect air quality in the surrounding area, and may cause health concerns.” It issued a local health advisory urging people with respiratory conditions to stay indoors and anyone experiencing “respiratory distress” to get medical help immediately.

The fire broke out in an area housing a number of oilfield services companies. Red River maintains rail spurs for loading and unloading liquids, such as crude oil, chemicals and pipes and related dry goods. The site also provides storage for various blending and delivery of drilling fluids, according to the company’s website.

A state health department spokesperson said the agency has inspectors at the scene where two of four buildings in the Red River complex are being allowed to burn. The health inspectors will monitor air quality, soil and groundwater impacts when the situation allows it, he said.

“It is our understanding that the company supplies various types of chemicals to the oil industry, and the fire officials on the scene are just letting the fire burn out,” the spokesperson said.

Local news reports from Williston described “occasional fireballs accompanied by the sounds of explosions” in the early morning hours Tuesday, along with thick black smoke above “towering” flames. A call to Red River’s Williston Basin office was not immediately returned.

Because of the fire and related smoke clouds, the Federal Aviation Administration issued temporary flight restrictions as of 8:30 a.m. CDT Tuesday for an international airport in the area, Stoulin Field.