Man suffers serious burns after assisting with fire rescue

A FIRE hero is battling serious burns after a Boxing Day blaze in Sydney.

The man, aged in his 30s, and two elderly residents were hurt and more than 50 people were evacuated from the suspicious house fire in Casula about 1am on Friday.

Police are investigating the townhouse fire.

Emergency services were called to the home on Myall Rd after residents reported smoke coming from the building.

"A man, aged 30, attempting to assist with evacuating residents has cut his left arm. He was treated at the scene by ambulance paramedics and taken to Liverpool Hospital in a serious condition," a NSW Police media spokesperson said.

"Two elderly residents were treated at the scene for smoke inhalation.

"Police believe no one was in the townhouse at the time of the fire."

Police said the fire was suspicious.