Early reports were that a natural gas leak could have caused a devastating explosion Sunday morning that killed two and injured as many as 100 at a power plant being built south of the city on the Connecticut River.

Homeowners more than 10 miles away said the 11 a.m. explosion at the Kleen Energy Systems power plant on River Road created a shock wave so intense they mistakenly thought the central part of the state had experienced an earth quake.

Medical rescue personnel said two were dead at the site and, of 100 so injured, four were in critical condition.

"There are bodies everywhere," a witness said. Another witness said many victims may be buried in rubble.

Middletown deputy fire marshal Al Santostefano said at 1:15 p.m. there were "confirmed fatalities" but that he did not know who many. He said there were at least 50 construction workers on the site.

"It was a massive explosion" he said.

Several patients were taken to Middlesex Hospital. One was transferred to Hartford Hospital and one was treated for minor injuries and released.

Six were still being treated for "multiple injuries" in the emergency room as of 2:15 this afternoon, said hospital Spokesman Brian Albert. The injuries include broken bones, orthopedic injuries and bruises; they are not considered critical, he added.

"We expect that we will be admitted two or three of those patients,'' Albert said.

Hospital officials are planning a press conference at 2:30.

Immediately after the incident, the hospital activated its disaster response plan. Albert said he has received calls from media outlets around the globe.

The plant, which has been under construction for years, was nearing completion. It was designed to generate electricity by burning natural gas. Neighbors said the explosion was the result of an operating test.

Santostefano said the explosion was related in some fashion to natural gas, but that the cause was still under investigation. He said the explosion appears to have occurred when operators attempted a "blow down" of natural gas pipelines, a procedure that involves the purging of gas from the pipelines..

Publically available information compiled by state regulators during the Kleen Energy plant approval process said that plant would operate on natural gas using a combined cycle turbine. Such turbines reuse waste heat produced the power generation process, increasing the plant's efficiency.

The plant operators proposed that when sufficient supplies of natural gas were not available, the plant would operate on low sulfur fuel oil.

The project was proposed mostly for the benefit of power consumers in the Middletown area, according the to publically available information.

Kleen Energy Systems received approval to generate 520 megawatts -- enough electricity for 364,000 to 520,000 households -- in November 2002 from the Connecticut Siting Council. As of 2006, the company was petitioning the Siting Council to be able to produce 620 megawatts. A megawatt is enough to serve 700 to 1,000 homes.

Neighbors of the plant said as many as 100 employees may have been working there when the explosion took place. A witness said the explosion took place when workers switched on the plant's energy generating systems during a test. Confirmed information about damage, injuries and the cause of the explosion was difficult to obtain.

Eddie Reilly, president of building trades council in Hartford, said Sunday there were more than 50 tradesmen on site Sunday morning.