A "bomb cyclone" has lashed Australia's most populous state with heavy rain and strong winds, forcing airlines to cancel domestic flights and prompting evacuation warnings in coastal communities.

Sydney weather has turned, and millions are in the path of a bomb cyclone bearing down on New South Wales. Here's everything you need to know.

The effect of a "bomb cyclone" around the New South Wales coastline is being felt north, in Queensland. Parts of the state experienced wind gusts averaging between 60 and 70 kilometres an hour overnight. Unlike in New South Wales, it is bringing cold but dry conditions to much of the state that could continue until Monday.