A strong earthquake rocked Niigata prefecture and a wide area of eastern and northern Japan including Tokyo at 10.40am local time on Wednesday 27 October.
The trembler follows a string of quakes that began on 23 October and have to date killed at least 31 people, forced more than 100,000 people into evacuation shelters and caused disruption to a number of factories in the area operated by Japan's major electronics companies.
The latest quake, the strongest since 24 October, had a magnitude of 6.0 and was centred 10km under central Niigata, according to Japan's Meteorological Agency. It was powerful enough to shake buildings in Tokyo, about 250km to the south.
The weekend quakes were centred on Ojiya in Niigata prefecture, where both Sanyo Electric and Matsushita Electric have factories. The Sanyo plant produces system LSI chips for some of the company's audio-visual products and the Matsushita plant produces the company's Panasonic-brand combination copy and fax machines.
Both factories have yet to be restarted following the 23-24 October earthquakes and the companies have not been able to fully ascertain the damage to the facilities.
The string of earthquakes, Japan's deadliest in a decade, began with a magnitude 6.8 shaker on the evening of 23 October and were followed within the next two hours by 10 strong quakes.
Martyn Williams writes for IDG News Service