Some workers on site have said on social media the second-storey floor collapsed as concrete was being poured early this morning.
Up to seven people fell 2.5m. Four were taken to North Shore Hospital with moderate injuries, a St John Ambulance spokeswoman said, and three were treated at the scene.
A police spokeswoman told the New Zealand Herald a number of people suffered minor injuries, but that no one was trapped.
Carpenters and concrete workers say a building being constructed by Haydn and Rollett was having concrete poured on the second floor when it suddenly caved in.
The building is close to the North Shore District Court.
At the site, several workers are standing around an area taped off with orange cones and yellow "caution" tape.
Workers can be seen pointing up towards the back of the building, part of which appears to have caved in slightly.
Parts of scaffolding equipment has been scrunched up as a result.
Workers declined to speak to media, but it appears all work has stopped for the meantime.
A sign outside shows the site is due to become an IAG Office Development.
Police said WorkSafe had also been contacted.
