TORONTO -- The apartment building where three people died in a fire was not legislated under the Ontario Fire Code as a senior's home, despite being advertised as a "senior's lifestyle suite" and only being available to people aged 59 and over.

For that reason, the building hadn't been inspected since 2013, fire officials say.

"This is an apartment that houses individuals who are older than 1/859 3/8 so there is no provincial legal requirement for any municipal fire departments to conduct routine inspections at these types of occupancies. They would be under retirement homes and long-term care homes, but this building does not fall under that classification," Toronto Deputy Fire Chief Jim Jessop told a news conference Saturday.

Police say three people are dead, and at least 12 others are being treated in hospital for various injuries following the fire at the building.

Paramedic spokesman Peter Rotolo says four people were taken to hospital in critical condition after the Friday afternoon blaze -- three have been pronounced dead.

The fire marshal is investigating the cause of the fire and the condition of the five-storey building where it took place.

Jeff Tebby, a spokesman for Ontario's Fire Marshal, said most of the damage was in a fifth floor hallway area. He said the building met fire code requirements on sprinklers but investigators were going to investigate whether smoke detectors were adequate. There was no immediate indication that the residents couldn't move out of danger quickly enough due to their age.

"Age is not necessarily a contributing factor that we're aware of," Tebby told reporters Friday night. "If that becomes a factor we will address it down the road."

A fire spokesman says some of the seniors were brought down ladders because the hallways were too full of smoke.

In the Ontario Fire Code, "homes for the aged" and "rest homes" are regulated as health care facilities, like hospitals. They have a higher standard of safety than a traditional house or apartment building.

But officers from the Toronto Fire department said that this building was not legislated as a senior's home, despite being advertised as a "senior's lifestyle suite" and only being available to people aged 59 and over. Because the province doesn't consider the building a senior's home, it was not subject to provincially-mandated fire code inspections, fire officials say.

Toronto Fire Captain David Eckerman said that the best course of action in an apartment fire is to "shelter in place".

"Everyone who's died in an apartment fire in the city of Toronto has either been in the unit where the fire started or in the hallways ... or the stairways, and overcome by smoke," he said.

Eckerman said in Friday's blaze, heavy black smoke filled the hallways. Some people had to be brought down on ladders because the hallways were so smoky.

"The smoke was so thick, a healthy young person couldn't have got through," he said. And that sort of thick, dark smoke can be full of carbon monoxide and carcinogens, he added.

Residents have been allowed to return to apartments on the first four floors.

Toronto Mayor John Tory visited the scene until early Saturday and praised the actions of emergency responders.

Tory said in a statement that the real danger in a fire is more from smoke that the fire itself.

"I hope we can learn any possible lessons as to how people, especially those more vulnerable, can be better protected in circumstances such as this," he said.