Around noon, an explosion occurred inside an intermodal container on a railcar at Union Pacific’s Bailey Yard in North Platte, though it wasn’t clear what caused the explosion, railroad spokeswoman Robynn Tysver said. No one was injured, and no cars derailed.

Authorities evacuated everyone within a one-mile radius of the explosion in the western end of the railyard because of the smoke, and U.S. Highway 30 was closed between North Platte and Hershey. Interstate 80 wasn’t affected by the smoke. It wasn’t immediately clear how many homes were included in the mostly rural area that was evacuated on the edge of the city. North Platte, which is about 230 miles (370 kilometers) east of Denver and about 250 miles (400 kilometers) west of Omaha, has a population of about 23,000.

The railroad said the fire had been extinguished by 5:30 p.m. Thursday. Earlier, the North Platte Fire Department said in a in a post on X the evacuations were done because of the fire at the railyard involved “heavy toxic smoke.” Fire officials didn’t immediately respond to a call seeking more details.

One of the containers involved was carrying perchloric acid, which is used in explosives as well as a variety of food and drug products, Tysver said. The car that exploded had been stationary for a couple hours beforehand, authorities said.

Joanna Le Moine, deputy director of the Lincoln County Emergency Management Agency, said officials are monitoring the situation and the weather to determine which direction the smoke will go “to help keep responders and citizens safe out of an overabundance of caution.”

The railyard where the explosion happened covers 2,850 acres (1,153 hectares) and stretches as wide as eight miles (13 km) at one point. A few years ago, an eight-story tall observation tower was built to allow people to watch thousands of railcars be sorted from one train to another on Union Pacific’s key east-west corridor.

One of the volunteers who was working inside the Golden Spike Tower Thursday told the North Platte Telegraph newspaper that he saw a “big ball of flame” billow up while he was talking to someone.

“And then it was just fire, fire, fire, constant for 10, 12 minutes maybe. And then the fire went down and smoke kind of increased, and then it was just sparks coming out,” Gregg Robertson told the newspaper.

Two plumes of smoke rose from the blast site, Robertson said. “The east plume was like black smoke. The west plume was orange smoke, something like I’ve not seen from a fire,” he said.

Railroad officials said that because the explosion happened near the western end of the railyard and the prevailing winds were carrying the toxic smoke outside the railroad, Union Pacific was able to continue operating part of the facility and keep trains moving. Once the fire was extinguished Thursday evening, Union Pacific was able to resume use of the entire railyard, spokeswoman Kristen South said.

Railroad safety has been a key concern nationwide ever since a Norfolk Southern train derailed and caught fire in eastern Ohio. That derailment prompted evacuations and calls for reform from members of Congress and regulators.

The National Transportation Safety Board is monitoring the situation but hasn’t started an investigation, agency spokeswoman Sarah Taylor Sulick said.

Federal Railroad Administration spokesman Warren Flatau said officials from that agency are at the railyard monitoring Union Pacific’s response to the explosion.