An explosion at an unfinished power plant in the US killed at least five workers and injured a dozen or more.
The explosion, at the Kleen Energy Systems plant in Middletown, Connecticut, could be heard and felt for miles.
Deputy Fire Marshal Al Santostefano said that no one was known to be missing amid the rubble from the damaged plant.
Still, crews planned to spend all night going through debris in case there were any more victims. The cause of the gas explosion was unknown, but tests on the plant were being carried out at the time.
A large swath of the structure was blackened and surrounded by debris, but the building, its roof and its two smokestacks were still standing.
Rescue crews had set up several tents alongside the site, which is a few miles from Wesleyan University on a wooded and hilly parcel of land overlooking the Connecticut River.
The explosion happened around 11.15am, Santostefano said. Mayor Sebastian Giuliano heard the blast while leaving church.
"It felt almost like a sonic boom," Giuliano said at an evening news conference.
Santostefano said 50 to 60 people were in the area at the time of the explosion, and multiple contractors were working on the project, making it difficult to quickly account for everyone.
The 620-megawatt plant, which was almost complete, is being built to produce energy primarily using natural gas. Santostefano said workers for the construction company, O&G Industries, were purging the gas line when the explosion occurred.
Officials had not released the conditions of the other injured people by last night, although they said at least a dozen people had injuries ranging from minor to very serious.
Kleen Energy Systems LLC began construction on it in February 2008. It had signed a capacity deal with Connecticut Light and Power for the electricity produced by the plant, which was scheduled to be completed by mid-2010.
Energy Investors Funds, a private equity fund that indirectly owns a majority share in the power plant, said it is fully cooperating with authorities investigating the explosion. In a written statement, the company offered sympathy and concern and said it would release more information on the explosion as it becomes available.
Daniel Horowitz, a spokesman with the US Chemical Safety Board, said the agency is mobilising an investigation team.
Plants powered by natural gas are taking on a much larger role in generating electricity for the US. Gas emits about half the greenhouse gases of coal-fired plants and new technology has allowed natural gas companies to begin to unlock gas supplies that could total more than 100 years at current usage levels.
Natural gas is used to make about a fifth of US electricity.