Rescue workers searched the largely unstable building for one person still unaccounted for on Saturday.

Nearby buildings were evacuated. An 82m construction crane - one of two still looming over the multistorey building - was also dangerously unstable, fire officials said.

The hunt for the missing was suspended at nightfall over safety concerns. A statement from the project contractor said its representatives would work "throughout the night" with emergency officials on a plan to stabilise the building.

"I heard a huge noise and thought it was a plane crashing," said Sue Hurley, a 68-year-old guest at a hostel across the street that shuddered with the force of the collapse. Hurley said she was reminded of news accounts of the 9/11 terrorist attacks.

WWL-TV aired and tweeted a viewer's dramatic video of upper floors falling on top of each other before one side of the building crashed to the street.

Another video on social media showed what looked like a metal structure - part of the building or a piece of construction equipment - tumbling to the ground and people running from the scene as clouds of dust billowed up, obscuring the view like a thick fog.

"I'm not sure what happened, but they told us to get out of here," said Michael Arbeiter, 30, from Munich, Germany, a hostel guest who said he was just getting out of the shower when his room shook. "Thank God it was not another 9/11."

Officials said 18 people were taken to the hospital and several others went to the hospital on their own. They said none of their injuries was believed to be life threatening.

Australian Associated Press