Queenslanders are being told to brace for the most catastrophic storm ever to hit their shores.
State Premier Anna Bligh said she did not think Australia had ever seen a storm of this intensity in an area as thickly populated.
She predicted it would be a very frightening time, with 24 hours of terrifying winds, torrential rains, and the likely loss of electricity and mobile phones.
Meteorologists upgraded Cyclone Yasi to a category five storm.
With winds of almost 300km/h (186mph), they are warning it poses an extremely serious threat to life and property, especially around the cities of Cairns and Townsville.
She warned that it could cause a tidal surge as high as nine metres (nearly 30ft), overwhelming low-lying coastal areas.
She said it would be a difficult night and a tough few days for the people of north Queensland, adding: "We are in completely uncharted waters.