A train carrying hazardous materials, including ammonia, derailed and caught fire near a rural North Dakota town on Friday, leaving officials puzzled about what caused it.

The 3:45 a.m. derailment impacted 29 cars of a Canadian Pacific Kansas City (CPKC) train, sending them off the track in a marshy area surrounded by farmland near the tiny town of Bordulac, Fox News reported. 

Both the train’s engineer and conductor escaped without injury, but there is concern about the materials and flames potentially harming the surrounding area and people. The cause of the derailment is unknown at this time. 

The cars were carrying anhydrous ammonia, sulfur, and methanol, and North Dakota Department of Environmental Quality spill investigation manager Bill Suess said that the most dangerous of those is ammonia. 

High levels of ammonia can irritate and burn the skin, mouth, throat, lungs, and eyes, according to the Centers for Disease Control and Prevention (CDC). Very high levels of ammonia can lead to lung damage or even death. 

Andrew Kirking, the emergency management director for Foster County, said that between ten and 15 cars caught on fire. 

Video shared by local farmer Doug Zink shows the flames raging just five miles southeast of his property:

Kirking told Valley News Live that by the next morning, the fire was mostly extinguished, and there was zero air contamination detected.

“An Environmental Quality report also says there are no impacts to soil of [sic] water outside the incident site,” the local outlet noted.

Kirking added that cleanup operations will continue through Saturday. 

CPKC said in a statement that Fox News obtained that it has “initiated its emergency response plan and launched a comprehensive, coordinated response.”

The National Transportation Safety Board (NTSB) has opened an investigation into the matter:

It was just over a year ago when a 70-car CPKC train, which was also transporting hazardous materials, derailed in Richland County, North Dakota. No injuries or fires were caused by that incident, according to Fox News.