Japanese government experts have warned that a mega-quake as large as the 2011 disaster may hit the country's northernmost region within the next 30 years.

An "impending" earthquake is forecast to strike off the Pacific coastline of Hokkaido, Japan's northernmost island, most likely triggering a massive tsunami, within the coming three decades.

The government's Earthquake Research Committee predicted a 70 per cent chance of a magnitude-8 to 8.6 earthquake hitting the Nemuro area in eastern Hokkaido within this timescale.

The panel also cited a 7 to 40 per cent likelihood of a magnitude-9 earthquake across the eastern Hokkaido region within the next three decades, with potential impact on nearby Aomori Prefecture, home to nuclear power plants.