North Carolina officials are asking thousands living within a one-mile radius of a raging fire at a fertilizer plant in the city of Winston-Salem to evacuate Tuesday amid fears of a large explosion. 

The fire started Monday night at Weaver Fertilizer Plant on North Cherry Street, and the City of Winston-Salem officials have confirmed small explosions at the plant.

In the most recent update provided around 9 a.m. Tuesday, Winston-Salem Fire Chief Trey Mayo said an estimated 500 tons of ammonium nitrate was in building, about 100 tons of ammonium nitrate was in an adjacent rail car and about 5,000 tons of finished fertilizer was at the site when it caught fire. 

The priority in the daytime was to continue to send drones into the air to monitor the fire and to continue to monitor the air quality outside the one-mile radius from the plant. 

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"We are not out of the woods. We've got about a 36-hour window where explosive potential exists. And we are about 14 hours into that," Mayo said. 

Matthew Smith, the leader of the on-site hazmat team, said the amount of nitrous gas in the air was not measuring close to what would be considered dangerous to life and health. 

Winston-Salem firefighters fought the blaze for about two hours before the fire "began affecting a rail car" and at that point "became an explosive hazard," prompting concerns of an explosion of ammonium nitrate, Battalion Chief Patrick Grubbs, a 15-year veteran of the Winston-Salem Fire Department, told reporters at the scene at about 4:30 a.m. Tuesday. 

"We're asking everyone to stay out of this area and evacuate the scene," Grubbs said, adding that an estimated 6,000 residents lived within a one-mile radius of the plant. 

Bright orange flames could be seen shooting into the sky along with thick plumes of smoke as lights from firetrucks and other first responder vehicles surrounded the fully engulfed building.

After those initial two hours, firefighters were pulled out and Emergency Management was called in. They then began accessing the scene every 15-20 minutes using drone teams from other fire departments, Grubbs said. Firefighters could not flow enough volume of water to be reasonably certain that they could keep it cool enough to prevent a detonation.

He said that once a railcar at the rear of the structure had become involved, they were unable to get water to the scene, so they decided to pull away because it had become a large explosive hazard.

As of early Tuesday, water was being pumped at the back of the location from a fire hydrant, Grubbs said.

"Don’t wait for something to happen. Something has happened," Mayo had said on Twitter. "Now is the time to get out."

According to a Winston-Salem Police Department news release, the 4400 block of Cherry Street from North Point Boulevard to Indiana Avenue was closed while emergency crews, including about 90 firefighters and 150 others from different agencies, responded to the fire around 8:20 p.m. on Monday. 

"We won’t be leaving the area anytime soon," Grubbs said Tuesday of his fire crews. But he asked that everyone stay out of the area and warned that there was going to be a lot of smoke and poor air quality.

Mayo said Monday evening that fire crews "abandoned" the fire-fighting operation because of the large volume of ammonium nitrate on site. The building had collapsed as well, and access to the product in the building was restricted, WGHP-TV reported.

At around 2 a.m. Tuesday, first responders were seen driving through the area asking residents to evacuate to safety as the threat of an explosion still loomed. Grubbs said first responders were also going door-to-door to get people safely away from the area.

"The evacuation area around 4440 North Cherry Street has almost 6,500 residents or 2,497 households," the City of Winston-Salem reported on its Twitter page.

Wake Forest University released a statement asking some students in off-campus housing to voluntarily evacuate. The university also said it is working on long-term plans for those who do not have an alternative place to go. The Forsyth Correctional Center is also included in the evacuation area.

Winston-Salem officials said a shelter has been set up at the Winston-Salem Fairgrounds. People who have evacuated should plan to be away from their homes for up to 48 hours.

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The fertilizer plant was closed when the fire started and no employees were inside, local media outlets reported. Grubbs said officials from the Weaver Fertilizer Plant have made no comment about the fire.

No injuries have been reported, and the cause of the fire is still under investigation.

The Associated Press contributed to this report.