An unknown number of people were killed and potentially hundreds injured Wednesday night in a massive explosion at a fertilizer plant in the U.S. state of Texas.

The exact number of casualties has not been confirmed due to difficulties in accessing the plant and the size of the explosion.

ABC, CNN and the Associated Press reported that there were two explosions at the fertilizer plant near Waco at 8 p.m. and 10 p.m. Wednesday.

A Texas Public Safety Department spokesman told ABC that about 200 people were injured in the explosion and 40 of them are believed to have been fatally injured. The spokesman, however, added that the number of deaths is undetermined.