ORILLIA, Ont. - Eight people remained in hospital Tuesday following a devastating fire in a central Ontario nursing home that left two residents dead.

The fire at the Muskoka Heights Retirement Residence in Orillia, Ont., on Monday sent 13 people, including the two dead, to Orillia Soldiers Memorial Hospital.

While three remained in hospital in Orillia, five others were transferred to the intensive care units of other hospitals in the province.

Provincial police identified the two men killed in the blaze as Robert McLean, 90 and Hugh Fleming, 85.

Ontario's fire marshal has assigned 10 people to investigate the cause of a fire.

"This organization will pour whatever resources we need to put into it to determine the cause and all the information surrounding the fire," provincial fire investigation manager Jim Fisher said Tuesday at a news conference in front of the blackened building.

The severe structural damage to the building, frigid temperatures and water still frozen inside the building will make for a slow-going investigation, said Fisher.

"There's a lot of valuable evidence in there that we're going to want to retrieve to determine the cause of this fire," he said. "But the process will be extremely slow."

Heavy equipment will be brought in to assist in carefully dismantling the building, said Fisher.

"We will take our time meticulously so we don't miss anything."

Based on observations made from an aerial ladder, the fire appears to have begun in the centre of the building, said Fisher.

But because floors have collapsed, investigators are not yet certain on what level of the two-storey building it might have broken out, he added.

Investigators will also look into all fire safety requirements, evacuation procedures, and escape routes under the fire and building codes and will be interviewing residents, staff and others involved, said Fisher.

The privately run home reportedly did not have a sprinkler system, as the province's fire protection act doesn't require sprinklers in private nursing homes.

NDP critic Andrea Howarth says the deaths could have been prevented if the government had implemented recommendations made after a similar fire in 1995. A coroner's inquest into eight deaths at the Mississauga facility recommended making sprinklers mandatory in all private retirement homes.

Fire officials have pressed the government in the past for such regulations.

A spokeswoman for Community Safety Minister Rick Bartolucci said he's open to changes and is reviewing all options.

"An alarm system was activated at the time of the fire," said Fisher.

The Ontario government says it's looking at possible safety changes, adding that regulations requiring sprinklers in new multiple-unit residential buildings more than three storeys high come into effect next year.

Ontario Fire Marshall Pat Burke expressed his condolences to the family and friends of the deceased.

Burke also congratulated firefighters, police and paramedics who responded rapidly to the emergency and got everyone out of the burning building.

Muskoka Heights, which neighbours say was at least 50 years old, was home to 23 residents.

Two of the residents were not at the home during the time of the fire.