EAST PALESTINE, Ohio (AP) — Authorities were threatening to arrest anyone who doesn’t leave an evacuation zone near the smoldering wreckage of an Ohio train derailment near the Pennsylvania state line and warned Monday there was a high probability of a toxic gas release.

While crews were working to prevent a major explosion, residents were packing overnight bags, loading their pets into cars and searching for hotel rooms. Police in the village of East Palestine moved out of their communication center as the threat of an explosion increased.

“I’m worried about leaving and not getting back,” Mallory Burkett, who lives just outside the evacuation area, said Monday just before her family drove out of town. “I’m definitely going to come back, but I’m not sure when.”

Officials warned hundreds of residents who had declined to evacuate earlier to do so Sunday night, saying a rail car was at risk of a potential explosion that could launch deadly shrapnel as far as a mile.

About 50 cars, including 10 carrying hazardous materials, derailed in a fiery crash Friday night, according to rail operator Norfolk Southern and the National Transportation Safety Board. No injuries to crew, residents or first responders were reported.

Norfolk Southern said 20 of the more than 100 cars on the train were classified as carrying hazardous materials — defined as cargo that could pose any kind of danger “including flammables, combustibles, or environmental risks.”

The cars involved carried combustible liquids, butyl acrylate and residue of benzene from previous shipments, officials said.

Five were transporting vinyl chloride, which is used to make the polyvinyl chloride hard plastic resin in plastic products and is associated with increased risk of liver cancer and other cancers, according to the federal government’s National Cancer Institute.

“There is no indication that any potential exposure that occurred after the derailment increases the risk of cancer or any other long-term health effects in community members,” said a post on the village’s Facebook page.

Authorities on Monday did not say what hazardous materials they were concerned about releasing into the air or how imminent that could be.

A statement from Ohio Gov. Mike DeWine’s office warned on Sunday night of “the potential of a catastrophic tanker failure” after a “drastic temperature change” was observed in a rail car.

Police cars, snow plows and military vehicles from the Ohio National Guard blocked streets leading into the village Monday morning as authorities began enforcing what had previously been a strongly recommended evacuation zone within a 1-mile (1.6-kilometer) radius of the crash site.

Schools and many businesses were closed, and the local high school was turned into a shelter.

Norfolk Southern has opened an assistance center in the village to gather information from affected residents. But some residents complained about a lack of information regarding the evacuation, which covered the homes of about half the town’s 4,800 residents.

Emergency responders were monitoring but keeping their distance from the fire. Remediation efforts could not begin while the cars smoldered, authorities said.

Federal investigators say the cause of the derailment was a mechanical issue with a rail car axle.

The three-member train crew received an alert about the mechanical defect “shortly before the derailment,” Michael Graham, a board member of the NTSB, said Sunday. Investigators identified the exact “point of derailment,” but the board was still working to determine which rail car experienced the axle issue, he said.

Mayor Trent Conaway, who declared a state of emergency in the village, said one person was arrested for going around barricades right up to the crash. He warned people to stay away and said they’d risk arrest.

“I don’t know why anybody would want to be up there; you’re breathing toxic fumes if you’re that close,” he said, stressing that monitors of air quality away from the fire showed no levels of concern and that the town’s water is safe.