Four nuclear power plants closest to Friday's powerful 8.9-magnitude earthquake that struck off Japan's northeastern coast have been safely shut down, the International Atomic Energy Agency (IAEA) said.

The Vienna-based U.N. atomic watchdog said its Incident and Emergency Centre received information from the International Seismic Safety Centre (ISSC) at around 0815 CET this morning about the earthquake of magnitude 8.9 near the east coast of Honshu, Japan.

The four Japanese nuclear power plants closest to the quake have been safely shut down, the agency said in a statement.

The IAEA had sent a so-called offer of good offices or assistance to Japan, should the country request support, it said. Current media reports say a tsumani alert has been issued for 50 countries, reaching as far as Central America. The agency is seeking further information on which countries and nuclear facilities may be affected.

IAEA said it has offered its support to the Japanese government.