Thousands of people at the top of New Zealand's North Island were told to evacuate on Thursday while an Australian town is forecast to be underwater later in the day as the tail end of Cyclone Debbie continues to cause major flooding.

The effects of the Category 4 storm, one level shy of the most powerful Category 5, are still being felt in both countries more than a week after it pounded Australia's Queensland state, killing six people, smashing tourist resorts, bringing down power lines and shutting down coal mines.

Scores of roads were closed or blocked by landslips across New Zealand's North Island following two days of heavy rainfall, although some areas had been given a reprieve from expected flash flooding. The international airport in the capital of Wellington was reopened on Thursday morning after the severe weather brought down air traffic systems late on Wednesday.