Image: 7 News Sydney

A gas explosion in Sydney’s west has left two men in a critical condition.

It’s taken more than 50 firefighters to put out the blaze at the factory on Warren Road in Smithfield, where two men have suffered severe burns.

They have been transported to Royal North Shore Hospital in a critical condition.

The flames caused damage to a nearby building.

Listener Paul tells Chris Kenny he heard a “massive” bang from across the road.

“It was a massive explosion, I was just getting in my car at the construction site nearby and the car shook. It was very loud.”

Click PLAY below to hear the full call

Motorists have been advised to avoid the area and the Cumberland Highway is closed northbound at Percival Road.

Claire Price from NSW Ambulance tells Chris reports from crews at the scene say it’s “a very serious situation”.

One male patient has burns to 36% of his body, including his airways, and a second man has burns to 18% of his body.

“They’re working incredibly hard on the scene to try and stabilise them before we transport them to hospital.”

Click PLAY below to hear from NSW Ambulance