Faulty phone charger may have sparked aggressive house fire

A fire that tore through a Sydney home this morning, sending a family of five fleeing, may have been sparked by a faulty phone charger.

9NEWS understands a phone charger in the front room may have sparked the blaze, in Mt Pritchard in Sydney's south-west.

The fire started just before 8am, and was well alight when Fire and Rescue NSW arrived.

The family of five inside had been alerted by a smoke alarm, as they were preparing to go to school and work.

A man, a woman and their three children - two aged in their 20s and a girl, 13 - were lucky to get out just before the roof collapsed.

They were checked over by paramedics and were in the care of family and friends.

The dramatic blaze saw flames shooting from the roof before it collapsed.

"Firefighters had to conduct an extremely aggressive attack on the fire, on all sides, to protect those houses," said Inspector Kernan Lambert from NSW Fire and Rescue.

The home ended up with 80 per cent fire damage and the remainder smoke damaged.

Fire investigators are now on the scene, but must tread carefully as there remains a risk the entire structure will collapse.