The Kleen Energy plant on River Road in Middletown, Connecticut, is seen Sunday Feb 7, 2010. An explosion blew apart the power plant under construction as workers purged natural gas lines, killing multiple people and injuring at least 14 in a blast that shook homes miles away, officials said.

NEW YORK: A huge explosion ripped through a US power plant on Sunday being built in Connecticut amid reports up to 50 people may have died, emergency officials said, as a rescue operation swung into place.

The blast at the gas-fired plant in Middletown, home to 40,000 people on the Connecticut River, sent flames and black smoke billowing into the sky and shook houses several miles away, witnesses said.

As helicopters, ambulances and fire trucks rushed to the scene and a massive search and rescue operation was launched, officials were reluctant to say how many might have died, but a large number of fatalities were feared.

“The reports vary from a few, several to possibly as many as 50 dead,” Brian Albert from the Middlesex hospital, which was treating several of those injured in the blast at the Kleen Enery plant, told AFP.

“They are in the process of search and rescue,” Albert said, adding that the Middlesex was treating six patients and a seventh had been transferred to the nearby Hartford hospital, which confirmed it was also handling injured.

One witness told the local Hartford Courant newspaper: “There are bodies everywhere.” Other witnesses suggested many victims could still lie buried in the rubble.

“There was a massive explosion, there are multiple injuries and possible fatalities,” Middletown police spokesman George Yepes said.

The Hartford Courant reported that helicopters were airlifting some of the victims to nearby hospitals.