Elderly woman's incredible escape from house fire

A massive blaze consumed a 70-year-old woman's home in Sydney's south - but her smoke alarms allowed her to make a lucky escape.

Adriana Oyhantcabal was unhurt, but could only stand and watch as her home was completely destroyed.

"It was huge, absolutely huge," one neighbour said.

Fire and Rescue NSW's Wayne Challinor said it was "very lucky" Ms Oyhantcabal had got out.

"I believe she had a working smoke alarm, which is fantastic, which we encourage everyone to have," he said.

The ruin of the home has been officially declared a crime scene.

Police are trying to establish whether the fire was deliberately lit.