Massive '10th alarm' fire contained after destroying two buildings in central Sydney

Firefighters say a massive blaze that engulfed a vacant seven-storey building in central Sydney has been contained.

Fire and Rescue NSW said its teams had "gained the upper hand" on the major fire, which has destroyed two multi-storey buildings in Surry Hills.

The massive inferno — dubbed a "10th alarm", the most severe type of fire — sent plumes of smoke drifting over the city and shut down nearby streets as the larger heritage-listed building started to collapse.

READ MORE: Witness accounts from the ground

Hundreds of people were evacuated from the area as the fire burned through several levels on Randle Street near Central Station just after 4pm.

Some sections of the exterior walls crumbled onto the pavement below.

More than 100 firefighters were called to the scene from multiple stations across Sydney, needing hours to battle the blaze with a combination of aerial and ground attacks.

"A short time ago, FRNSW's incident controller declared the fire is contained," the organisation said in a statement issued just before 7pm.

"[Firefighters] successfully stopped the blaze from engulfing other nearby buildings, including residential apartments."

However, operations will continue throughout the night and an exclusion zone remains in place, with FRNSW urging the public to avoid the area.

Authorities warned people living in the vicinity of the fire to keep their windows and doors closed to prevent potential impacts of smoke.

NSW Fire and Rescue Commissioner Jeremy Fewtrell said earlier that the building was made out of "well seasoned and dry timber" with significant airflow between the levels, which is what caused the building to burn with such speed and intensity.

"The information we have at this stage was the buildings were vacant or unoccupied, whether they were under construction or about to have sort of demolition or work done," he said.

Initial reports suggest the building was abandoned but hundreds of people in nearby apartments and office buildings were evacuated.

Firefighters then worked to contain a new secondary blaze at a neighbouring building.

Fire alarms went off in surrounding buildings after sensing the smoke, which Fewtrell said contributed to everyone evacuating safely.

"We have some engineers attending the scene and they'll help guide our decisions around safety considerations, particularly around the risk of collapse," Fewtrell added.

"We will make the assessments on a building-by-building basis to determine when it's safe and the conditions that are safe for them to return."

'Bloody scary'

One woman who was near Central Station at the time told 9News she was "a bit in shock".

"I was right there and it was very loud," she said.

One student said he felt a wave of heat move across his face.

"It was bloody scary when it collapsed," he said.

"It was really loud and I was scared for the people who were around there.

"The wave of heat that came on my face, it was scary."

Witnesses on the ground during the evening commute described the chaotic scene.

"Probably one of the biggest building fires I've seen in the city," 9News senior cameraman Mike McGee said.

"I first got off the train and saw the smoke.

"That was pretty much before any fire trucks or police had arrived.

"There were flames leaping out from every window."

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