More than 100 firefighters battled towering flames and thick smoke from a seven-storey blaze in central Sydney on Thursday as the fire service said it was spreading.
"The building is starting to collapse, while the inferno is beginning to spread to several neighbouring buildings, including residential apartments," the fire and rescue service for Australia's New South Wales region said.
The entire top floor wall leaned over and crashed in pieces into the street below, fire service video showed, as the building glowed orange with flames.
Hoses poured water down the building, all of its windows lit by flames.
The carcass of a flaming van was parked in front.
Images posted on social media showed flames almost as high as the building itself shooting into the sky.
Emergency services said they sent more than 100 firefighters, with 20 fire engines, who were "working to contain and extinguish the blaze" on Randle Street near the city's Central Station.
"The public is urged to avoid the area as firefighting operations continue," the fire service said, as the sound of emergency vehicle sirens echoed through the city streets.
One firefighter received a minor burn to his right arm, the service said.
Firefighting operations are expected to continue throughout the night.
"Terrible fire in Surry Hills in my electorate. Please stay safe and listen to instructions from emergency services," politician Tanya Plibersek said in a statement on Twitter.
Light rail services near the blaze were suspended until further notice, New South Wales Transport said.
A spokesperson for the New South Wales Police said there were currently no reports of injuries.
Burning embers were also swept on to a balcony of a nearby building, television footage showed.