The fire erupted at 8.50pm on Monday, January 8, at a home on Cullen Drive, with firefighters from across the Illawarra racing to the scene.

"Smoke and flames were visible and an elderly couple had self-evacuated," Fire and Rescue NSW Inspector Greg Purvis said of the moment crews arrived.

The fire was burning with such intensity that firefighters were unable to enter the property.

"It was too dangerous to go in when we got there," Insp Purvis said.

Firefighters fought the blaze from outside the home and frantically worked to protect neighbouring homes.

Next door neighbours Wayne and Kerrie Cox rushed to move their car from beside the burning house as Mr Cox grabbed a garden hose.

"By the time I got the hose and started hosing down my roof it [the burning house] just went bang. I was worried they [his neighbours] were inside," he said.

His neighbours are Anita and her husband Frank, both aged in their 70s, who fled their burning home with nothing more than the clothes they were wearing.

They were assessed by paramedics, but were uninjured.

Mandy Chaplin lives across the road and was in the shower when she heard loud bangs before realising her neighbour's house was burning down.

"I heard bangs, but not massive explosions. I thought the neighbours were doing something in their garage," she said.

"When I saw the house on fire, I ran out in my towel and I was yelling out. I just panicked."

The quick actions of firefighters prevented the blaze from spreading to neighbouring properties.

Anita and Frank have lived in their Cullen Drive home for decades and they noticed a smell of smoke before realising there was a fire burning inside their house.

"They smelt some smoke and went down to investigate and then when they opened the door to the garage, found the fire in the garage," Insp Purvis said.

"The top floor is pretty well totally destroyed, there is smoke damage all through the bottom floor of the premises.

"If this had happened later at night when they were asleep it could have been a totally different outcome."

A NSW Police forensic investigator was at the burnt-out home the following morning to determine how the blaze stared.

Insp Purvis said it may take some time for the cause to be identified.

"Due to the large amounts of flammable liquids and fuels that you normally find in a garage, investigations are ongoing to try and determine exactly what started the fire," he said.

Firefighters are so concerned about the number of house fires in the Illawarra, they are providing free smoke alarms (including free installation) and fire safety advice for residents.

There is no catch, the smoke alarm is free and so is the fire safety advice.

For more information head to www.fire.nsw.gov.au