Five people are known dead and at least 12 injured in a deadly explosion occurred Sunday at a power plant in Middletown, Connecticut State of the United States.

Police seal off the road to the blast site at the Kleen Energy plant in Middletown, Connecticut, the United States, Feb. 7, 2010. (Xinhua/Gu Xinrong)

He, however, said the exact number of casualties is not yet available as it is not known how many workers were at the site when the explosion occurred at the Kleen Energy Plant at about 11: 30 local time.

Earlier, Al Santostefano, the deputy fire marshal in Middletown, told local media Hartford Courant that at least 50 construction workers were on the site when the explosion occurred.

“Multiple contractors were on site - adding to the confusion on the number of employees actually working on site,” the mayor’s office said earlier in a statement.

The power plant is not yet fully on line and the explosion occurred during a testing procedure, the statement said.

People who live around 20 miles away reported having felt the explosion which many mistook for an earthquake.

VietNamNet/Xinhuanet