More than 130 firefighters battled towering flames and thick smoke as a huge blaze consumed an unoccupied seven-storey building in central Sydney, today.

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.

The fire had also spread into another "abandoned and derelict" three-storey building.

Officials said that the inferno had a "10th alarm" status, the most severe type of fire.