Two powerful earthquakes, one measuring 7.8 on the Richter scale, jolted the northern Japanese island of Hokkaido early Friday, triggering extensive power outage and a fire in an oil refinery, Kyodo news agency reported.

At least five people were reported injured by falling furniture, it said.

A JR Hokkaido express train derailed in Onbetsu. It was not immediately known whether there were injuries.

The first earthquake, which struck at around 0450 hours (local time), centred in the Hidaka and Tokachi region, the Japan Meteorological Agency said. The second quake struck at 0607 hours.

Hokkaido is the northernmost and most sparsely populated of Japan's major islands. Sapporo is the prefecture's capital.