An earthquake with a preliminary magnitude of 6.7 and a number of aftershocks rocked Japan's Hokkaido prefecture, Japan Meteorological Agency (JMA) said, with one person found with no vital signs.

The major temblor was centered in the Hokkaido prefecture at 3:08 a.m. local time Thursday (1808 GMT Wednesday), with the epicenter at a latitude of 42.7 degrees north and a longitude of 142.0 degrees east and at depth of 37 km, according to the JMA.

The earthquake logged upper 6 in some areas of Hokkaido prefecture on the Japanese seismic intensity scale which peaks at 7, according to the JMA.

Dozens of aftershocks followed, including one with a preliminary magnitude of 5.4 that hit the prefecture at 6:11 a.m. local time (2111 GMT Wednesday).

Japan's Nuclear Regulation Authority said that the Tomari nuclear power plant operated by Hokkaido Electric Power Co.' s, had lost an external power source, and a spent fuel pool of its reactors was currently being cooled by an emergency power supply system.

The JMA said there might be a slight sea-level change in Japan's coastal areas as a result of the 3:08 a.m. quake.

Local police said they had received multiple reports of injuries as a result of the quake, including an 82-year-old man who was found with no vital signs after falling down the stairs in his residence during the quake.

A number of houses in the quake-stricken areas have been confirmed collapsed, with rescue work under way for those possibly buried under the houses, according to local officials.

The quake has also triggered power blackouts across a wide area in Hokkaido affecting millions of households, and hundreds of thousands of households were reported with no water supply.

The Japanese central government has set up a liaison unit at the crisis management center of the prime minister's office to gather information on the quake.

Japan's weather agency warned that earthquakes with a similar magnitude might still hit the quake-struck region in the following week.