Millions of residents along Australia’s eastern coast are preparing for the impact of the most southerly cyclone to threaten the region in more than five decades.

Australia's east coast braced on Wednesday for a tropical cyclone that is swirling towards Brisbane, the country's third-most populous city, as authorities warned thousands of properties were at risk due to strong winds and flash flooding.

Satellite imagery can help determine the strength, size and cohesion of a storm. The stronger a storm becomes, the more likely an eye will form in the center. When the eye looks symmetrical, that often means the storm is not encountering anything to weaken it.