Mass casualities and multiple injuries were reported Sunday after a massive explosion at a Connecticut power plant, police confirmed to Fox News.

The explosion occurred just before 11:30 a.m. local time at the Kleen Energy plany on River Road in Middletown, Conn., according to authorities.

About 100 people were working at the plant during the time of the explosion.

Dozens of ambulances and fire trucks were on the scene and witnesses said black smoke could be seen for miles.

Police are advising everyone to stay away from the area.

The power plant was reportedly undergoing construction at the time of the explosion, though authorities said they do not know what caused it.