TOKYO – A strong earthquake with a preliminary magnitude of 6.8 jolted northern Japan early on Thursday, but there was no threat of a tsunami from the quake, the Japan Meteorological Agency said.

The focus of the tremor was 120 km below the surface of the earth in Iwate prefecture.

National broadcaster NHK said some parts of highways had been closed to traffic and some rail lines were stopped after the quake in the region, which is a mountainous and sparsely populated part of Japan.

An Iwate prefecture official said there had been no reports of initial damage, though some city halls had reported that that some panes of glass had broken in their buildings.

Tohoku Electric
9506.T{QR}said its nuclear facilities in the area were operating normally after the quake, except for one unit that was already off-line for maintenance work.

Japan's Jiji news reported that the government had set up an emergency task force at the prime minister's residence following the quake.

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.

Thursday's quake follows a string of earthquakes in the same region, the first of which in mid-June killed at least 10 people and left as many again missing.

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.