Circular Quay railway station and nearby buildings have reopened following the huge blaze at the former Gold Fields House site in Sydney's CBD, which is now contained, although commuters are facing transport delays due to the fire.
A frightening warning came across screens at the station during peak-hour this morning with the text "Emergency. Evacuate now".
Other screens stated: "Emergency. Walk to the nearest exit now and leave the station."
Trains did not stop at Circular Quay as firefighters contained the blaze at the construction site in Alfred Street, which is located just metres away from the station and the Cahill Expressway.
It is understood scaffolding on the site went up in flames at 8.45am, trapping workers at the top of the building at the time.
It has since been confirmed that the inferno was caused by an accident involving an oxy LPG torch that was being used to cut steel at the base of the site. In that process, molten steel came into contact with the plastic scaffolding sheeting and sparked the flames.
There was also a number of explosions on the site, with the fire belching thick black smoke into the city's sky.
The Gold Fields House was built in 1966 and was one of Sydney’s earliest high rises.
In 2014, the property was sold to Chinese investors for $425 million, who also bought the Fairfax House and The Rugby Club.
The three blocks have been consolidated where two new towers will be built - one for residential use and the other as a hotel.
At 10.30am, Fire & Rescue NSW confirmed there was still an active fire but it was contained.
A total of 20 fire trucks and more than 60 firefighters were called to the scene to tackle the raging fire.
Thirteen people have been treated for smoke inhalation.
“It’s been upgraded to a fourth-alarm response, which is quite a big response,” a Fire & Rescue NSW spokesman told 9NEWS this morning.
“All people were evacuated and no inquiries have been reported. The crews have said the outside sheeting of scaffolding was alight.
“There’s a lot of smoke in the area and a lot of traffic around the CBD at 9am. An exclusion zone is in place at the moment.”
At midday, workers were allowed to return to work.
The Cahill Expressway has reopened but other roads remain closed.
Motorists and pedestrians are advised to avoid the area and public transport passengers are advised to allow extra travel time and listen to announcements.
Train services are returning to normal but delays are still expected and some services around the network have been cancelled, a Sydney Trains spokesperson told 9NEWS.
"The delays are due to a fire earlier today at Circular Quay, which resulted in us having to close the entire city circle for safety reasons. This caused significant disruption to our services across the network," a Sydney Trains statement said. "As a result of this, there have been some cancellations and changes to timetabled services on the T1 North Shore, Northern and Western, T2 Inner West and Leppington, T3 Bankstown, T5 Cumberland and T8 Airport and South lines. This means customers may experience extra travel time due to these service gaps.
"Buses are supplementing train services at Bankstown, Blacktown, Campbelltown, Glenfield, Hornsby, Lidcombe and Olympic Park."