A number of people are feared dead after a massive explosion at a US power plant yesterday.

Around 250 people are also thought to have been injured in the blast at a gas-fired power station in Middletown, Connecticut.

It is thought a gas pipeline exploded, triggering devastation on a large scale. Homes were shaken and the main building of the power station flattened, according to some witnesses. The plant was being built by Kleen Energy Systems.

There was confirmation last night that five people had lost their lives — but rescuers who are combing the wreckage of the plant feared more bodies would be found.

At least four of the injured were also in critical condition.

Brian Albert, a spokesman at Middletown's Middlesex hospital, said: “They are in the process of search and rescue.”

Tremors caused by the explosion at the plant, which is located on the Connecticut River, could be felt up to 50km away. Many thought it was an earthquake. According to one witness, there were “bodies everywhere” and others said more victims could be buried in rubble.

A gas pipeline was said to have exploded and flames were seen shooting out of it.

The explosion was believed to have happened during a test of generating systems at the 620 megawatt gas-fired power station.

The new plant would have been one of the largest in Connecticut, and up to 1,000 people had been working on its construction. It was due to come online on June 1.

Police officer Kevin White said he did not know how many people were on site but said there were “mass casualties”.

The college town of Middletown is around 30 miles south of Connecticut state capital, Hartford.

Fire department deputy marshal, Al Santostefano, said there were 50 workers on the site at the time of the blast. “It was a massive explosion,” he said.

The explosion occurred at the back of the largest building on the site, he said. “It's possible that there might be people trapped in the rubble. There was a lot of steel, from what I could see.”

Rescue teams, including dogs, were looking for survivors.