(CNN) — Residents near the site of a train derailment that sparked a massive fire in East Palestine, Ohio, were urged to evacuate immediately Sunday night due to the risk of an explosion, authorities said.

“Within the last two hours, a drastic temperature change has taken place in a rail car, and there is now the potential of a catastrophic tanker failure which could cause an explosion with the potential of deadly shrapnel traveling up to a mile,” Gov. Mike DeWine warned in a statement Sunday.

The train crashed Friday while carrying hazardous materials and led to a large inferno that continues to burn, which has also prompted concerns about air quality.

The governor said that crews are working to prevent the explosion, but nearby residents must leave immediately. While most people in the one-mile radius have already evacuated, more than 500 people have declined to leave their homes, according to local officials.

Anyone who stays in the area could be arrested, Columbiana County Sheriff Brian McLaughlin said, warning that, “There is a high probability of a toxic gas release and or explosion.”

“We need to get everybody who remained within that mile radius — or decided they needed to come back within that mile radius — we need you to leave now,” Fire Chief Keith Drabick said.

The fire chief said there was a “drastic change” in the vinyl chloride — a chemical the train was hauling that officials had been concerned about.

“This catastrophic failure, if it occurs, it will produce hydrogen chloride and phosgene gas into the atmosphere,” Drabick said, adding that the mile-radius around the derailment may be extended.

Gov. DeWine activated the Ohio National Guard Sunday evening to deploy to the scene to assist local authorities.

Officials are also monitoring the environmental impact caused by the derailed train.

Trent Conaway, the mayor of East Palestine, assured residents earlier that the air and drinking water remain safe after the Norfolk Southern train crash. He said classes at East Palestine schools would be canceled Monday, as would city meetings.

The train derailed in East Palestine, about 15 miles south of Youngstown, according to earlier comments by officials. Of the more than 100 cars, about 20 were carrying hazardous materials, according to the National Transportation Safety Board, which is investigating the incident.

Ten of those cars derailed, including five that were carrying vinyl chloride, the NTSB said in a statement Saturday. The agency said so far it had “not confirmed vinyl chloride has been released other than from the pressure release devices.”

While air and water quality remained stable Sunday, and officials have yet to see abnormal levels in screenings, “things can change at any moment,” said James Justice, an on-scene coordinator with the EPA’s Emergency Response.

Authorities continue to monitor for a “long list” of chemicals, he said — not only those provided to authorities in a list from Norfolk Southern, but also those that can result from combustion.

Officials issued a shelter-in-place order for the entire town of roughly 5,000 people, and an evacuation order was issued for the area within a mile radius of the train crash near James Street.

Both restrictions remained in place Sunday, Conaway said at an earlier news conference. Drabick told reporters at the news conference the scene remained volatile, preventing authorities from conducting on-scene operations. Crews will not be able to determine the full list of chemicals involved until the fire stops burning, Drabick said.

Officials urged residents to follow the shelter-in-place orders. On Saturday evening, one person was arrested for misconduct after approaching the scene and getting too close to the train, the mayor said.

“Please stay home. I can’t reiterate it enough,” Conaway said. “Do not come to our town.”

The Ohio EPA is monitoring water quality in local streams, which eventually feed into the Ohio River, a spokesperson said, but the agency does not anticipate contamination to East Palestine’s public water system, which draws from other sources.

The agency installed containment dams in area streams and set up three aeration locations using high volume pumps to treat water and remove dissolved contaminants.

In an email to CNN Sunday morning, a spokesperson for Norfolk Southern deferred all questions to the NTSB.

Correction: A previous version of this story misspelled Keith Drabick’s last name.

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