Construction site on fire in Sydney CBD

Julia Carlisle

Scaffolding covering a high-rise construction site in the heart of Sydney has caught fire, with dramatic footage showing flames and smoke shooting up the building.

The fire started at the Macquarie Street building, near Hyde Park, about 7.50am Thursday, with fire crews racing to the scene and closing the street.

Footage from Network Nine shows flames quickly rising up the 11-storey building, sending a plume of black smoke into the sky.

"About 20 people have been safely evacuated," a Fire & Rescue spokesman told AAP.

Thirteen fire crew and 70 firefighters are on the scene.

"The fire has been confined to the external scaffold, it hasn't penetrated the internal structure," he said.

"The fire is under control but not completely extinguished."

NSW Police said there have been no reported injuries. Diversions are in place.