A fire that's left a man with critical burns to 60 per cent of his body is under control after ripping through a chemical disposal factory in Sydney's west.
Firefighters are monitoring the atmosphere for dangerous chemicals near the building on Links Road at St Marys, a NSW Fire and Rescue spokesman told AAP.
The injured man, 55, was airlifted to the Royal North Shore Hospital where he remains in a critical but stable condition.
Large amounts of smoke billowed out of the building, and up to 70 firefighters were called in to contain the blaze which started just before 9am on Monday.
It's not yet known what sparked the fire but reports indicate it may have involved a processing machine and aerosol cans exploding inside the building, a NSW RFS spokesman said.