Two men seriously burnt after explosion at western Sydney factory

Two men have been taken to hospital with serious burns after an explosion and fire at a factory in Sydney's west.

Emergency services were called to the factory complex on Warren Road, Smithfield, about 4.20pm on Tuesday.

A NSW Ambulance spokeswoman said six crews attended and treated two men at the scene with serious burns, one with burns to 36 per cent of his body, the other with 18 per cent burns.

Both men have been taken to Royal North Shore hospital in a serious condition.

There have been reports the explosion and subsequent fire was caused by a gas bottle, however NSW Police said in a statement that extensive damage to the building means it will take some time for the cause and origin of the fire to be determined.