AS many as 50 people are said to have been killed in a huge explosion at a US energy plant in Connecticut, a hospital spokesperson said.
Witnesses told the local Hartford Courant newspaper that as many as 100 people were injured in Sunday's blast at the Kleen Energy plant on the outskirts of Middletown on the Connecticut River.
"There are bodies everywhere," one witness was quoted as saying while others said victims may be buried in the rubble of the plant which was still under construction.
Officials would not immediately confirm any deaths or the number of injured, while CNN was reporting at least two fatalities.
"There was a massive explosion, there are multiple injuries and possible fatalities," Middletown police spokesman George Yepes said.
Dozens of emergency personnel swarmed around the sprawling energy complex after the explosion, which rocked nearby residential housing shortly before 11:30am local time, 3.30am this morning Melbourne time.
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The Hartford Courant reported that 20 ambulances were at the scene and said helicopters were airlifting some of the victims to nearby hospitals.
While US media reports talked of "mass casualties" at the gas-fired energy plant in Middletown, a spokeswoman at the main Middlesex Hospital nearby said they had not seen any deaths and had received less than 20 injured so far.
She told AFP an emergency command centre was being set up to deal with the incident. "We don't know what we've got at the moment," she added.
"There was an explosion at a Kleen Energy plant," Middletown Fire Department commissioner Bill Gregorio said. "There are some," he responded when asked about the number of injured.
Pictures of the site showed a convoy of ambulances driving into the facility, from which a huge, gray plume of smoke rose into the sky.
AFP could not immediately contact officials at the plant.
One witness told the Hartford Courant that the explosion took place during a test of the plant's power generating systems.
The 620-megawatt Kleen Energy plant, said to be one of the largest power facilities to be built in New England for many years, was still in the process of being built.
The gas-fired energy production plant is located on the outskirts of the city on the edge of the river, but close to some residential housing.
A company called Energy Investors Funds recently acquired 80 per cent of the Kleen Energy, which had been due to go online sometime in 2010.