Under the Environmental Planning & Assessment Act 1979, development can become State significant development (SSD) in two ways.
First, a State Environmental Planning Policy may declare any development, or class or description of development, to be SSD.
Most State significant development is identified in the State & Regional Development SEPP, and includes:
development from certain industries (mines, factories, power stations, schools, hospitals), generally due their size, economic value or potential impacts; and
development on sites with strategic planning significance (Barangaroo, Darling Harbour, Sydney Opera House, Sydney Olympic Park).
Other SEPPs (such as the Three Ports SEPP) also identify SSD.
Second, the Minister for Planning may declare specified development on specified land to be SSD by order published in the Government Gazette. However, prior to making such an order the Minister must first obtain advice from the Independent Planning Commission about the State or regional planning significance of the development and make this advice publicly available.