EAST PALESTINE, Ohio: After a freight train carrying hazardous chemicals derailed in Ohio near the Pennsylvania state line on February 4, authorities launched a federal investigation and monitored local air quality.

The rail operator, Norfolk Southern, reported that a train with some 100 cars, which was carrying a variety of chemicals from Madison, Illinois, to Conway, Pennsylvania, derailed in East Palestine at around 9 p.m.

No injuries or damage to structures were reported, and there was no immediate information about what caused the derailment.

Meanwhile, Michael Graham, a member of the National Transportation Safety Board, told reporters, "The post-derailment fire spanned about the length of the derailed train cars. The fire has since reduced in intensity, but remains active and the two main tracks are still blocked," as reported by the Associated Press.

Norfolk Southern said 20 of the more than 100 cars were classified as carrying hazardous materials, defined as cargo that could pose dangers, "including flammables, combustibles, or environmental risks."

"At this time we are working to verify which hazardous materials cars, if any, have been breached. The Environmental Protection Agency and Norfolk Southern were continuing to monitor air quality, and investigators would begin their on-scene work "once the scene is safe and secure," Graham said.

Before declaring a state of emergency, citing the "train derailment with hazardous materials," Mayor Trent Conaway said air quality monitors throughout a one-mile zone in which residents were evacuated had shown no dangerous readings.

Freezing temperatures in the single digits complicated the response as trucks pumping water froze, he added.

Fire Chief Keith Drabick said emergency crews would keep their distance until Norfolk Southern officials told them it was safe to approach.

Officials said that firefighters were ordered to pull back from the immediate area and unmanned streams were used to hose down the site.