A huge explosion has rocked a power plant in the US state of Connecticut, killing¹ at least five people and injuring 12, the local mayor has said.

美国康乃迪克州一座发电站发生巨大爆炸，造成至少5人死亡、12人受伤。

The 620MW Kleen Energy plant was due to come online in the summer

Middletown Mayor Sebastian Giuliano said it was caused by a gas explosion.

People living up to 50km (30 miles) away reported that their homes were shaken by the blast at the Kleen Energy plant, being built outside Middletown.

There are reports of people trapped under the remains² of a plant building, and a rescue operation is under way.

Search experts and specialist dog teams were at the site combing through the wreckage³（残骸） , the mayor said.

Speaking at a news conference on Sunday evening, Mr Giuliano said that the identities of the dead had not yet been released as some of the victim's families had not yet been informed.

Mr Giuliano said the plant, which was only 95% complete and due to open fully⁴ in the summer, was undergoing（经历，忍受） a series of gas tests when the explosion occurred.

He said between 100 and 200 people worked on the massive site, and were employed by multiple contracting（缔约的，承包的） companies.

"How many people were here today - that's the number they can't really nail down（确定，明确） . They were purging⁵ gas lines all night long, most people were evacuated⁶（撤离，疏散） from the building when they ran the tests," Mr Giuliano said.

The plant is located to the south of the town, on the Connecticut River.

Earlier, deputy fire marshall（火警部门） Al Santostefano said there were some 50 construction workers on the site at the time of the explosion.

At least 100 firefighters were sent to the scene and it had taken them an hour to contain the fire caused by the blast, he said.

Officials say there is no further danger to the public, and have not evacuated the area. The plant, however, remains cordoned⁷ off（隔离，戒严） .

The nearby Middlesex Hospital told the Associated Press it had received 11 victims, while the hospital in the state capital, Hartford, has treated three others.