UPDATE 1-Strong quakes strikes northwest Japan, tsunami warning issued

An earthquake with a preliminary magnitude of 6.8 struck Japan's northwest coast around Niigata prefecture on Tuesday, with shaking strong enough to damage buildings and prompting a 0.2-1.0 metre tsunami warning, There were no immediate reports of damage, although areas hardest hit by the quake could not be contacted by telephone, according to public broadcaster NHK.

Tokyo Electric Power Co's Kashiwazaki-Kariwa nuclear plant was not affected by the quake, which hit 85 km ( 53 miles) northeast off the coast, with all of its seven reactors already shut down, NHK said. The quake struck at 10.22 p.m. local time (1322 GMT Thursday) at a depth of 10 kilometres. The U.S. Geological Survey (USGS) put the magnitude of the quake at 6.5.