UPDATE 9.45am: The Cahill Expressway has reopened over Circular Quay but Pitt Street remains closed southbound between Bridge and Alfred Street.
With regards to public transport, buses are no longer diverting but are delayed up to 15 minutes through the area. Trains are still not stopping at Circular Quay Station but ferries continue to operate to and from Circular Quay.
A building at Circular Quay has been engulfed in flames after an explosion on the ground floor, according to reports.
Multiple fire crews are at the scene, with video footage showing the outside scaffolding of the Pitt Street building well alight.
All people have been evacuated, Fire and Rescue NSW has confirmed, and there are no reported injuries.
Sydneysiders are advised to avoid the area, with access to Bridge Street from Loftus Street cut-off.
George Street is also closed between Bridge Street and Alfred Street.
More as we get it.