The Ontario Fire Marshal is investigating a fire at a dollar store in Listowel, in southwestern Ontario, that claimed the lives of two volunteer firefighters.

The blaze broke out on Thursday around 3:30 p.m. at the Dollar Stop in the town's centre. Witnesses say the fire appeared to start on the roof of the building, where work may have been taking place.

Listowel Volunteer Fire Department members Raymond Walter, 30, and Kenneth Rea, 56, were killed when they entered the fire-engulfed store to search for any shoppers left inside. It appears part of the roof collapsed on top of the men.

Ontario Provincial Police eventually searched the building and found the men's bodies. They were removed from the site a day later, before a crowd of about 100 onlookers and dozens of firefighters standing at attention.

Chris Williams with the Ontario Fire Marshal's Office said that a structural engineer had been called in to advise on how to safely recover the bodies. Some of the walls of the building were "at risk of collapse," he said.

When not working for the volunteer fire department, Rea worked at a car dealership. On Friday, his wife Louise told southwestern Ontario radio station AM980 that her husband was dedicated to his family and the fire department. The couple had three children and three grandchildren.

"He was very family oriented; he loved his kids; he loved family," Rea said. "He loved the fire department -- that was his life."

Walter was also married and worked as an accountant.

Several politicians have offered their condolences to the men's loved ones.

Prime Minister Stephen Harper said that he "was deeply saddened" to learn of their deaths.

"These were remarkable individuals -- heroes who volunteered to do life-threatening work to keep their communities safe," Harper said in a statement.

Premier Dalton McGuinty called the deaths tragic and "a solemn reminder that we must never take their sacrifices for granted," he said in a statement, referring to volunteer firefighters.

On Thursday night, North Perth Mayor Julie Behrns said the men's deaths had saddened the community.

"We thank all of our volunteer firefighters and their families for their dedication protecting us," she said.

Oxford MPP Ernie Hardeman, who spent 25 years as a volunteer firefighter with Southwest Oxford, said the news hits home.

"It's just hard to imagine what they must be going through and the pain of all the 'what ifs," he said of the men's families. "Volunteer firefighters give their time to help neighbours... and firefighting is a family."

Listowel is about 200 kilometres west of Toronto.

With files from The Canadian Press