At least 6,000 residents are being asked to evacuate their homes over fears of an explosion after a fire broke out at a fertilizer plant in the North Carolina city of Winston-Salem.
The fire at the Winston Weaver Co. fertilizer plant was still active as of around 4:30 a.m. ET, Winston-Salem Fire Department Battalion Chief Patrick Grubbs said at a news conference early Tuesday morning.
"We're asking everyone to stay out of this area," he said, as officials told residents within a 1-mile radius of the plant to evacuate the area.
About 220 minimum security offenders were also evacuated from Forsyth Correctional Center in Winston-Salem, according to a statement from the North Carolina prison system. The inmates were taken to an empty minimum-custody unit around 60 miles away.
The fire broke out on Monday evening, according to officials. It is unclear what caused the blaze. No injuries were reported as of Tuesday morning, when Winston-Salem Fire Chief Trey Mayo said the fire had been “relatively static” overnight.
But with 600 tons of combustible ammonium nitrate stored at the site, the risk of an explosion would remain through Wednesday, he said.
“We’ve got about a 36-hour window where that explosion potential exists” Mayo told reporters.
Capt. Matthew Smith of the North Carolina Hazardous Materials Regional Response Team 5 said crews were stuck in a "waiting game."
It's "not worth having firefighters go in and try to put the fire out," he said. "As fire burns we’re losing fuel so we’re getting into the decay phase and the risk goes down so if we just wait another 12 hours we’ll be in a better place."
Grubbs said Monday that crew "fought the fire for two hours" before the blaze "began affecting a rail car."
Once the rail car was involved, he said, "it became an explosive hazard," with the potential for an explosion of ammonium nitrate.
Ammonium nitrate is a chemical compound used as a source of nitrogen for fertilizer. It is also used to create explosives for mining, however.
That development forced firefighters to pull back, Grubbs said, with at least 90 firefighters involved in the effort.
He said first responders had been going door-to-door, telling residents to leave their homes. He said fire officials were assessing the scene "every 15 to 20 minutes."
In a separate statement shared on Twitter by the Winston-Salem Police Department, Fire Chief Trey Mayo warned residents not to "wait for something to happen."
"Something has happened. Now is the time to get out," Mayo said.
It was unclear whether any residents had refused to leave their homes, with Grubbs saying he did not have a number for refusals.
In addition to the evacuations, the blaze also forced the nearby Wake Forest University to cancel classes for Tuesday.
In an alert, the school said that staff who "are not needed to support the evacuation effort" were encouraged to work remotely.
The school said it had also opened up several sites, including the Wellbeing Center, Benson Center and ZSR Library for faculty, staff or students who are evacuating and need somewhere to go.
"Those buildings will remain open all night," it said.
In addition to fears of a potential explosion, Grubbs also said that air quality in the area would likely be poor in the midst of the fire. "As the sun rises, there's going to be a lot of smoke," he warned.
Authorities have not yet determined what caused the fire. The Bureau of Alcohol, Tobacco, Firearms and Explosives said Tuesday that its investigators would be assisting local firefighters.
Winston Weaver Co. did not immediately respond to a request for comment from NBC News.