Two people have been injured in a building collapse in Sydney.

The building on Wattle St in Ultimo caved in about 11am on Monday, causing debris to crash onto cars at a neighbouring petrol station.

WATCH THE VIDEO ABOVE: Wall collapse injures two at Sydney construction site

Paramedics told 7NEWS.com.au they are treating assessed seven people at the scene following the incident, which is being treated as a possible workplace incident.

Two men, aged in their 30s and 60s, were taken to hospital in serious conditions.

Footage from the scene shows a ute almost completely crushed in bricks while the frame of the building has been mangled.

Two firetrucks have been dispatched to the scene as firefighters check the stability of the remaining structure.

Police are also on the scene to establish a perimeter around the site.

The public have been urged to keep clear of the site as emergency services now begin work to safely enter the building.

More to come ...