The quake was centered in Iwate, a sparsely populated area around 300km north of Tokyo. Dozens of aftershocks also jolted the area.

At least four people were buried in a landslide at a hot spring resort in Kurihara city in hard-hit Miyagi prefecture, TV Asahi reported, though it was unknown whether they were dead.

Three more were missing at a work site after another landslide in Kurihara, Kyodo news agency said, adding that more than 100 people were hurt.

Water containing a small amount of radiation leaked within a Tokyo Electric Power Co nuclear power facility in the region, but there was no leakage outside, a spokesman for Japan's biggest utility said.

The energy released by the quake was far less than in the case of the magnitude 7.9 earthquake that hit southwestern China on May 12, leaving nearly 87,000 people dead or missing.

Earthquakes are common in Japan, one of the world's most seismically active areas. The country accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater, prompting tough building codes to try to limit damage.

In October 2004, an earthquake with a magnitude of 6.8 struck the Niigata region in northern Japan, killing 65 people and injuring more than 3,000. That was the deadliest quake since a magnitude 7.3 tremor hit the city of Kobe in 1995, killing more than 6,400.