Police and firefighters say they're investigating a woman's claim that her 13-year-old son accidentally started a fire that gutted part of their East Vancouver apartment building Wednesday.

The blaze broke out at about 11 a.m. in a third-floor unit at 1766 Frances Street near Commercial Drive.

A woman named Cheryl and her three children live in the unit where the fire started.

"My son accidentally done it," she told CTV News. "He lit a match and it accidentally fell on a big bag of laundry…so it all caught up in flames and that's how it started."

Cheryl was in the lobby of the building at the time. She said her boyfriend tried to put the fire out but turned his attention to getting the kids to safety when the flames started spreading.

Firefighters were still working to knock down the blaze by Wednesday evening.

"We're going to be here for a while," said Assistant Fire Chief Ray Bryant. "We won't go anywhere until it's out."

The 27-unit building is run by the Vancouver Native Housing Society. According to the group’s website, it is "designated for persons of Aboriginal ancestry only."

Firefighters say the building doesn't have sprinklers, but does have working smoke alarms.

Video from the scene showed thick smoke billowing out of the structure while residents stood outside in a staging area set up by firefighters.

"The whole apartment floor was engulfed in smoke," said resident Clifford Ryan. "I couldn't breathe—it was all black."

Officials say all 48 residents made it out safely and all the animals in the building have been accounted for, thanks in part to some heroic acts.

One man scaled the side of the building to get Cheryl's cat out of the burning apartment. The man and the animal both fell on the way down, but neither appeared seriously injured.

"I want to thank him very much, because I honestly though my cat was going to be dead," Cheryl said.

A firefighter also injured his shoulder while breaking down a door.

With files from CTV Vancouver’s Sarah MacDonald