Twelve fire crews were called in to fight the blaze at the site of the old Goldfields House Building. Some 24 construction workers at the site managed to escape without serious injury.
Emergency crews react to the Circular Quay fire.
As flames quickly spread, workers inside the building were evacuated, and witnesses reported several nearby buildings were also evacuated.
The work site supervisor has reported all workers have been accounted for.
Shareholders will give final approval for the sale in March this year.
A fire engulfed a luxury Sydney property development overlooking the harbour bridge on Tuesday, just two weeks after China's Dalian Wanda Group agreed to sell the site.
At about 11.45am, NSW Fire and Rescue said the blaze had been extinguished but an exclusion zone was still in place.
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A NSW Ambulance spokesman said one person is being assessed for smoke inhalation.
"We are now assessing 13 of the workers who were in close proximity to the smoke for potential respiratory issues", Ambulance Service Inspector Giles Buchanan said.
The fire is now under control and trains have resumed services to Circular Quay train station.
With regards to public transport, buses are no longer diverting but are delayed up to 15 minutes through the area.
Even the Cahill Expressway was closed over Circular Quay this morning, but has since reopened.
- Sunrise (@sunriseon7) February 12, 2018HUGE FIRE: Pitt Street near Circular Quay.