The fire department announced citizens within a one-mile radius of the plant should evacuate in case of an explosion. The Winston-Salem vicinity has almost 6,500 residents in nearly 2,500 homes.

“We want to make sure that right now we’re evacuating everybody in this one-mile radius,” Winston-Salem Battalion Chief Patrick Grubbs told reporters early Tuesday. “There is still a potential for explosion.”

Authorities drove through neighborhoods Monday night, knocking on doors and asking residents to leave their homes. Citizens are directed to the Education Building at the Winston-Salem Fairgrounds if they need a place to stay, according to Winston-Salem’s communications director Ed McNeil.

Wake Forest University canceled classes on Tuesday and announced it would be opening up three campus sites to shelter students who had to evacuate from their homes.

Officials said the fire started about 8:20 p.m. Monday. About 90 firefighters and 150 first responders fought the fire for nearly two hours before they were pulled back, Winston-Salem Fire Chief Trey Mayo said.

Mayo pulled the crews because of the large quantities of ammonium nitrate at the plant. If exposed to high enough temperatures, ammonium nitrate can trigger an explosion.

“We abandoned the firefighting operation because there is a large volume of ammonium nitrate on site and we could not flow enough volume of water into the area where that ammonium nitrate is stored to be reasonably certain that we could keep it cool enough to prevent a detonation,” Mayo said in a video on Twitter.

Mayo said the building had collapsed, so access to the chemical was tough. For the crews’ safety, they withdrew.

A Weaver Fertilizer spokesman on Tuesday said, “there have been no injuries or loss of life to any employees, fire responders or citizens at this time. We are grateful for the outstanding, rapid work last night and ongoing support from fire officials, as well as the volunteer services who have supported our employees and plant neighbors.”

Weaver Fertilizer plans to participate fully with authorities while they investigate the cause of the blaze.

Though a cause has not been identified yet, residents reported hearing two “tremendous” booms, The Charlotte Observer reported.

The Winston-Salem Fire Department said they are continuing to monitor the site. The department will be holding a live press conference at 4:30 a.m. Wednesday.