Fiji is bracing for a severe tropical cyclone with the potential to be one of the most destructive in history.

Cyclone Yasa is tracking north-west of Fiji's main island, Viti Levu, and is expected to directly hit both of Fiji's main islands as a Category 5 cyclone, the highest category for tropical cyclones.

The cyclone is expected to pass over the country on Friday with an estimated 600,000 people directly in the cyclone's path, based on tracking estimates from Tuesday night.