Tokyo, Aug 19 (IANS): Japan Friday issued a tsunami alert after a 6.8-magnitude undersea quake struck off the country's northeastern Honshu island, Xinhua reported.

The tremor occurred around 2.30 p.m., triggering a tsunami advisory for Miyagi and Fukushima prefectures of the Hondu island.

The quake caused a high-speed train in the region to suspend service and expressways to be closed.

No abnormalities were noticed at the Fukushima nuclear plant on the island, the operator Tokyo Electric Power Co. said.

The prefectures suffered massive damage in a quake and tsunami in March, triggering a nuclear crisis in Fukushima.

Earlier on Friday, another quake measuring 6.3 on the Richter scale jolted the Fiji Islands in south Pacific but there was no immediate report of damage or casualty.

The tremor occurred at 0354 GMT with the epicentre 16.5 degrees south latitude and 176.7 degrees west longitude, the Hong Kong Observatory said.