PASADENA, Texas -- A fire burned for hours at a Pasadena warehouse early Friday, KPRC Local 2 reported.

Pasadena firefighters said the fire started in the back of the warehouse, where an ammunition manufacturing business is located, on Shaver Street near Spencer Highway at about 2 a.m.

Investigators said an employee was melting lead inside the warehouse when the fire started. He escaped from the building without injury and called 911.

Crews arrived and battled the raging flames for three hours.

"Live rounds (of ammunition) fired several times and crews had to pull back while they tried to put out the fire," Pasadena Fire Department spokesman Mark Beaver said.

Hazardous materials crews went to the scene to deal with the chemicals inside and monitor the air quality.

Investigators said sodium cyanide was in the building. They are working to determine if that chemical played a role in the fire's ignition.

Residents at Shaver Landing apartment complex were evacuated and taken to South Houston High School.

"When I wake up I heard boom and explosions," evacuee Lenor Vasquez said. "I went and look at it and the flame was going."

A shelter-in-place was issued for Pasadena and Deer Park for a short time.

Many nearby streets were closed to traffic while crews battled the blaze.