A nuclear watchdog group says tens of thousands of people living outside the no-go zone around the Fukushima power plant in Japan should be evacuated.

France's Institute for Radiological Protection and Nuclear Safety says around 70,000 people living outside the Fukushima evacuation zone should be moved.

Its warning is based on radioactivity data collected by Japanese authorities and from US monitoring flights over the area.

The French watchdog says among those who should be evacuated are nearly 10,000 children.

Japan has already begun moving more than 5,000 people who live in villages well outside the 20-kilometre evacuation zone.