The mayor of the small Texas town where a massive explosion tore apart a factory and other nearby buildings Wednesday night says as many as 40 may be dead.

The Los Angeles Times reports that Mayor Tommy Muska said in a telephone interview that he arrived at the count of 35 to 40 dead because all other residents and first-responders in the area have been identified.

Other U.S. media report more than 170 injured were injured in the blast at the fertilizer plant.

Attention was initially drawn to whether Wednesday's explosion was another terrorist act in the wake of Monday's bombing at the Boston Marathon. However, investigations are now leaning towards the possibility that the explosion was caused by carelessness in plant operations and poor response measures.

U.S. media report the explosion likely occurred after firefighters sprayed water on anhydrous ammonia which was leaking from the fertilizer plant. Anhydrous ammonia is highly explosive when in contact with water.

Shortly after the explosion, a mushroom cloud was spotted from the air and tremors were felt in locations some 80 kilometers away from the site of the explosion.