WASHINGTON (Agencies) - A gas line exploded on Sunday at an under-construction power plant in Middletown, Connecticut, killing at least 50 people and injuring over 250 others. 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, told AFP. They are in the process of search and rescue, Albert said, adding the Middlesex was currently treating six patients and one other had been transferred to the nearby Hartford hospital. The local CBS station WFSB reported on its website: Police in Middletown said there was an explosion with mass casualties just before 11:30am (16:30 GMT) at the Kleen Energy plant on River Road. There was a massive explosion, there are multiple injuries and fatalities, said Middletown police office George Yepes. Medical rescue personnel said four of the injured were in critical condition, according to the Hartford Courant newspaper website. There are bodies everywhere, a witness said. Another witness told the paper many victims may be buried in rubble. Officer Kevin White of Middletown Police told Reuters he did not know how many people were on site at the time of the accident but there were mass casualties. He could not confirm fatalities. White said tests were being run at the time and the plant was new and had not gone on line. Scores of ambulances and several helicopters rushed to the scene of the Kleen Energy plant on the banks of the Connecticut River. Some might still be trapped under the rubble, and a search-and-rescue team was trying to find them, an official said. The explosion was felt in neighbouring towns as far away as East Haven, a distance of 30 miles, and black smoke was visible for miles around. I felt the ground shake and thought a tree had fallen nearby, said Ethan Goller, who at the time was working in his garage in Ivoryton, 12km from Middletown. A plant official told a local NBC TV station the facility was a 620-megawatt gas-fired power plant. This would make it a relatively small- to mid-sized plant, in which case the explosion would likely not have major market implications, an energy expert said. A spokeswoman at Middlesex Hospital told AFP an emergency command centre was being set up to deal with the incident. We dont know what weve got at the moment, she added. There was no further danger to the public, an official told reporters. Local hospitals were on mass casualty alert. Firefighter Cliff Seifert confirmed there were numerous casualties. State emergency official Betsy Hard said local authorities had asked the state for help.