Japan issued tsunami alerts on Monday after a series of strong quakes in the Sea of Japan.

The Japan Meteorological Agency reported quakes off the coast of Ishikawa and nearby prefectures shortly after 4pm, one of them with a preliminary magnitude of 7.6.

It issued a major tsunami warning for Ishikawa and lower-level tsunami warnings or advisories for the rest of the western coast of the island of Honshu.

Japanese public broadcaster NHK TV warned torrents of water could reach as high as 5m and urged people to flee to high land or the top of a nearby building as quickly as possible.

NHK said the tsunami waves could keep returning, and warnings were continuing to be aired nearly an hour after the initial alert.

The Government was set to hold a news conference later in the day. Reports of damage were not immediately available.

A tsunami of about 3 metres high was expected to hit Niigata and other prefectures on the western coast of Japan. Smaller tsunami waves were already confirmed to have reached the coastline, according to NHK.

The area includes a nuclear plant. Tokyo Electric Power Co, the operator, said it was checking for problems but there were no immediate reports of any irregularities.

Japan is an extremely quake-prone nation. In March 2011, a major quake and huge tsunami caused meltdowns at a nuclear plant.