(Wikimedia Commons)

Witnesses reported hearing a noise like an explosion before the buildings came down. The force was so powerful that it blew out the windows in neighboring buildings. The fire department is still determining the cause.

A spokeswoman for Con Edison, an electric provider in New York City, said a report came in just before the explosion from someone in the building who smelled gas. 

And tests relfect a high level of gas at the scene.