A GRANDMOTHER felt the heat of flames bursting through closed windows as she fled with her family before their Cairns home was engulfed in fire.

Joy Durie had been doing some washing in her downstairs granny flat when fire erupted in the upstairs kitchen in the McManus St home of her son and daughter-in-law at Whitfield about 1pm yesterday.

Ms Durie said fire spread quickly through the 1970s era weatherboard home, barely leaving her daughter-in-law and their four children enough time to grab their pets and run.

"We weren't able to salvage anything," she said.

"We barely got the dogs out of the yard. It was so fast.

"We could barely stand the heat of the flames breaking the front windows upstairs, while we got the dogs out of the front yard."

Three of the children, all teenagers, were treated at the scene by paramedics for smoke inhalation.

Ms Durie said everyone who was in the house at the time of the fire was uninjured, but the family was devastated they had lost all their belongings.

"I'm just thinking of everything in there, and we've lost the whole lot - even my shoes," she said.

"My watch, my laptop, everything - gone.

"Even photos, books, everything.

"We don't know what to do."

Queensland Fire and Emergency Services incident controller Clint L'Estrange said firefighters did not initially realise the family had managed to escape.

He said the top floor of the largely timber home was completely gutted.

The ground floor also suffered water and smoke damage and he said it would be "unliveable".

"The fire investigators will go there. We believe it was (started in) the kitchen," he said.

"It was unknown when we first arrived if anyone was trapped inside on arrival.

"It took us to about halfway through the job to realise.

"It was a pretty intense fire."

He said it took about 20 firefighters more than three hours to fully extinguish the blaze.

At least two firefighters had to be assessed by paramedics for heat exhaustion.