FREMONT, Neb. — Three people are missing and a fire continues to burn after a massive explosion Tuesday at Horizon BioFuels in Fremont.

The blast happened just before noon at the facility, which operates in the former Golden Sun Feeds building. Video shows smoke beginning to rise from the top of the tower, which looms hundreds of feet in the air. Flames appear soon after, spreading throughout the entire plant within seconds.

Nine fire departments responded with mutual aid, but Fremont Fire Chief Todd Bernt said an active fire persists in the tower. He expects crews to remain on site for several days.

Firefighters do not yet have safe access to the facility to conduct search and rescue operations for the three people who were at the plant at the time of the explosion. Nebraska Task Force 1 is assisting on scene.

“We had them come just due to the structural collapse that we had,” Bernt said. “Have them recon the area and be able to give us updates on how we can safely get into the structure and do a search for the missing individuals.”

According to its social media pages, Horizon BioFuels produces animal bedding, heating pellets and smoking pellets.

Officials have not said what caused the explosion. The Nebraska State Fire Marshal’s Office is on scene investigating.