Firefighters from Port Macquarie and Wauchope fire stations arrived at 3.42am to find the top level of a two-storey house completely engulfed in fire.

It took approximately 20 firefighters to extinguish the blaze.

The family was alerted to the fire thanks to a working smoke alarm, allowing them to escape the fire uninjured.

Fire and Rescue crews from Wauchope, Port Macquarie and a specialist HAZMAT team battled the blaze for almost an hour and a half, Fire and Rescue Port Macquarie Inspector Gaven Muller said.

The cause of the fire is now under investigation by police investigators.

"The occupants of this home are alive today due to the fact they had a working smoke alarm," Insp Muller said.

The risk of a fatality in the home is halved if there is a working smoke alarm. Yet, 50 percent of residential home fires attended by FRNSW do not have a working smoke alarm.

Insp Muller said the occupants - a man, woman and 11 month old child - are lucky to be alive.

"A working smoke alarm alerted them to the fire and allowed them to get out before it caused mass destruction," he said.

Superintendent Scott Dodson said this is a timely reminder to have at least one working smoke alarm installed on every level of your home, it is the law.

"A fire can take hold in just three minutes, so it is vital to have working smoke alarms in your home and to test them regularly," he said.

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