Firefighters have faced the biggest blaze of their careers when an inferno at a Sydney waste facility triggered an enormous explosion.

Dramatic footage shows a huge fireball erupting 150 metres into the night sky as 200 firefighters tackled the blaze at North St Marys, in the city’s west, around 11pm Saturday.

A large chemical tank was blown into the air and fist-sized chunks of concrete blocks rained down on the firefighting crews.

More than 50 fire units attended the blaze as crews battled the flames from all sides.

They established determined lines of defence from holes blown out of neighbouring buildings.

Fire and Rescue NSW said it was one of the biggest fires seen in western Sydney for many years.

Two firefighters suffered minor injuries to their hands at the height of the emergency.

“The real miracle was the fact that all of our people were able to stay safe through that very intense explosion,” Fire and Rescue NSW Commissioner Jeremy Fewtrell said.

“I have never seen anything like that, to that degree.

“I’ve had firefighters today tell me they’ve been in the job for almost 40 years and had never seen an explosion fire so big, so it was very significant.”

FRNSW units sent to the scene included five aerial platforms to battle the flames from above, while other fire trucks pumped water by relay to douse the flames.

Hazardous materials crews were also on hand, dealing with the subsequent chemicals being consumed in the fire.

The Environment Protection Authority was on scene, along with Police and NSW Ambulance.

Local residents were urged to stay away and close their windows, doors and vents during the emergency to avoid harmful smoke.