Officials said Friday that no one was injured. The danger to residents remains low, according to the county's disaster control agency, which reported no air pollution in the area or in the direction of the wind.

Twenty-nine cars of a CPKC train derailed around 3:45 a.m. in a swamp surrounded by farmland about 140 miles (225 kilometers) northwest of Fargo, county emergency management director Andrew Kirking said.

Kirking said in a statement Saturday that the fire still flares up occasionally as crews clear wagons from the tracks, but “the firefighting operations overnight and this morning have been incredibly successful,” he said.

Rescue workers now stated that the derailed wagons contained, among other things, ammonia, methanol and plastic pellets.

Bill Suess, head of the North Dakota Department of Environmental Protection's oil spill investigation program, cited ammonia as a potential risk, but winds carried the smoke away from the nearby town of Bordulac, which has a population of about 20.

“The wind was on our side here,” Suess said on Friday.

Exposure to high levels of ammonia in the air can cause burning of the eyes, nose, throat and respiratory tract and can lead to blindness, lung damage or death, health officials say. Exposure to lower levels can cause coughing and irritation of the nose and throat.

CPKC said in a statement Friday that it had “launched its emergency response plan and initiated a comprehensive, coordinated response.”

The railway was formed last year from the merger of the Canadian Pacific Railway and Kansas City Southern.

The National Transportation Safety Board said Friday that the incident was being investigated.