Emergency crews are on the scene of an explosion and fire at a power plant in Middletown. There are reports of mass casualties, but there are no confirmed details.

The explosion happened at the Kleen Energy natural gas and oil plant under construction on River Road around 11:30 a.m.

Two LifeStar helicopters were called to the scene. One has taken off carrying one patient. We do not know any details about the person's injuries.

There are reports there may have been 300 people in the building at the time of the explosion.

Bernadette Nyland was outside in her yard with her dogs when she heard the blast. "They were doing the firing of the engines this morning and so something went wrong and it blew up and flames came shooting up almost as tall as that stack," she said.

There are reports that homes near plant have been damaged by the explosion. It was felt as far away as Wallingford, North Haven, North Branford and Cheshire.

News Channel 8's Darren Kramer said on Twitter was outside in North Guilford when he heard the explosion. "Sound was huge and low. Lasted several seconds. Assumed sonic boom."

Another Twitter follower named Jennifer said via Twitter, "First thought was earthquake or huge gust of wind--whole house shook, very brief but powerful"

Others heard or felt the explosion in Oxford and as far away as Mystic. WTNH-TV