Crews battle massive demolition site blaze at Sydney's Circular Quay

Emergency crews are at the scene of a fire that broke out on a 10-storey demolition site at Sydney's Circular Quay.

The fire is at the corner of Pitt and Alfred streets where multiple crews are on the scene with many more on the way.

NSW Fire and Rescue spokesman, Superintendent Andrew Ticehurst, said the fire didn't appear to be escalating.

"It appears as though it's been extinguished outside the building but they're working to ensure it's completely extinguished inside," he said.

The fire broke out in Circular Quay at about 8.45am. Source: Twitter/ Jessica Ridley

"It looks like fire fighters are on top of it, but there will still be significant traffic delays in the area because of the smoke."

A thick, black smoke filled the air around Circular Quay after the fire broke out before 8.45am Tuesday where the curtain on scaffolding erected around the site caught ablaze.

A NSW Ambulance spokesman said one person is being assessed for smoke inhalation.

Train services were initially disrupted but have since resumed.

There were reports of loud explosions heard when the fire broke out.

Everyone in the building has been evacuated and seven crews are on scene fighting the fire.

More to come.