An Ontario man was among the five people killed in Sunday's explosion at a power plant under construction in Middleton, Conn.

Roy Rushton of Hamilton, Ont., shown in this undated photo, was killed Sunday with four other people in an explosion at a power plant in Middletown, Conn. (Courtesy of Global TV)U.S. authorities have identified him as Roy Rushton of Hamilton.

Also killed in the blast were:

• Peter Chetulis of Thomaston, Conn.
• Ronald Crabb of Colchester, Conn.
• Raymond Dobratz of Old Saybrook, Conn.
• Chris Walters of Florissant, Mo.

More than two dozen people were injured in the powerful explosion, which shook houses kilometres away. Hospital officials said most were treated and released.

A fire official said no one is believed to be in the rubble of the Kleen Energy Systems plant in Middletown, about 32 kilometres south of Hartford.

However, Middletown Mayor Sebastian Guiliano said rescue crews have been unable to get to all areas of the plant and he could not say for certain that no more victims would be found.

Authorities said one section of the plant was too unstable to search on Monday. They were also missing an exact roster of everyone on duty when the blast occurred.

The explosion at the Kleen Energy plant in Middletown, Conn., on Sunday shook houses for kilometres. Five died in the blast, but it's not clear if other workers are accounted for. (Catherine Avalone/Associated Press/The Middletown Press)The explosion happened as workers were clearing gas lines of air, but the exact cause remains under investigation. Authorities also launched a criminal investigation Monday, saying they could not rule out criminal negligence.

"I lost a couple of good friends up there," Michael Rosario, a business representative with the local Plumbers and Pipefitters union, said as he broke down crying Monday. "I'm just so sorry something like this happened.

"There's still a lot of unanswered questions," Rosario added.

Welders and other workers were at the site Monday, preparing to make it safer for emergency personnel, said Ed Reilly, president of the Greater Hartford-New Britain Building Trades Council.

Roster needed to confirm victims

Gov. M. Jodi Rell said Monday morning that officials still haven't received rosters of workers who were at the Kleen Energy Systems plant Sunday.

"There are a number of contractors who do the work at the building," Rell told WTNH-TV.

"Until we actually have a roster of the names of those individuals that are in each of those groups and who was working on Sunday, we need that before we can do anything else. We're still confirming the number of people," she said.

"There's still uncertainty about who came in and who didn't come in yesterday," Middletown Deputy Fire Marshal Al Santostefano added.

Michael Rosario, centre, business representative for the Plumbers and Pipefitters union, is comforted after telling reporters about losing three friends in the explosion. (Seth Wenig/Associated Press)

Santostefano also said there were "piles of rubble everywhere, debris everywhere. In some places the debris is as high as 10 feet."

Local fire investigators and federal authorities on Monday were expected to begin their investigation into what caused the explosion at the nearly completed 620-megawatt plant.

It was being built to produce energy primarily using natural gas, which accounts for about a fifth of the country's electricity. Workers for the construction company, O&G Industries, were purging a gas line, clearing it of air, when the explosion occurred around 11:15 a.m. Sunday, Santostefano said.

The blast left huge pieces of metal that once encased the plant peeling off its sides. A large swath of the structure was blackened and surrounded by debris, but the building, its roof and its two smokestacks were still standing at the site.

About 50 to 60 people were in the area at the time, he said.

With files from The Associated Press