Some 60 to 70 people were killed and hundreds were injured by an explosion at a fertilizer plant outside Waco, Texas, AFP reported citing local media.

The report could not be immediately verified, AFP said, but KWTX television cited West Emergency Management Services Director George Smith as confirming the death toll.

Firefighters responding to the scene were also injured in a secondary blast, according to radio traffic by emergency managers being broadcast by CBS News.

"There has been an explosion on the fire scene, there are firefighters down at this time," a dispatcher said.

A man on the scene reported that "the restroom is severely damaged we have many people down." Firefighters also said they were setting up a triage unit at an apartment building where people were trapped.

The explosion at the West Fertilizer plant occurred just before 8:00 pm (0100 GMT), Waco Assistant Fire Chief Don Yeager said.

The cause was not immediately known but he said it was an anhydrous ammonia explosion.

Fire departments from nearby jurisdictions rushed to the scene in the small town of West, north of Waco, where the blast was so powerful that it knocked down some nearby buildings, and set fire to others.