Billowing smoke from a pizza restaurant fire shut down parts of central Sydney, and about 1200 people were evacuated from nearby offices.
People were evacuated from a 20-storey building opposite World Square at 12.30pm (local time) today after a blaze in Macchiato Pizza Bar and Grill, firefighters say.
No one was injured.
It prompted the closure of the areas around Pitt St and Liverpool St, leading to gridlock on CBD roads.
Fire and Rescue NSW Superintendent Ian Krimmer says grease trapped inside an oven chimney may have caught fire, triggering the restaurant's sprinkler system and the building's fire alarm.
The restaurant sustained water and smoke damage, Supt Krimmer told AAP.
Tracie and Tim Mitchell walked past the building before the alarm was raised and noticed a light mist of smoke coming out of a first-floor vent of the building.
"The closer we got, it started to smell like burning brake pads," Ms Mitchell told AAP.
The Newcastle couple walked past the building again about 15 minutes later, when Ms Mitchell told her husband the smoke was getting worse.
"As soon as those words came out of my mouth there was just the biggest explosion of smoke," she said, and it became difficult to breathe.
"It was a big ball of the thickest, blackest smoke you can imagine coming straight for us," Ms Mitchell said.
"We were enveloped in it.
"You could hear the sirens but you couldn't seem them coming down the road."
A worker in a third floor office told AAP he saw the smoke first before he heard the evacuation alarm.
"The smoke was billowing, it was so thick," said the man who gave his name as Charlie.
"I can still taste it, it was thick, it was oily, it was vicious."
He said the evacuation was orderly and he was unaware of his workmates being overcome by smoke.
Footpaths around the building reopened at 2pm.
Police are investigating.
