TOKYO, July 30 (Xinhua) -- Japan's Meteorological Agency has downgraded tsunami warnings to advisories for the Pacific coasts of Hokkaido and the Tohoku region following a powerful earthquake off Russia's Kamchatka Peninsula earlier in the day.

The advisory for Okayama Prefecture has been lifted, but advisories remain in place from Hokkaido to Okinawa.

Authorities continue to urge residents to avoid coastal and river mouth areas, warning that elevated sea levels could persist for at least a day.

At Iwate Prefecture's Kuji Port, waves as high as 1.3 meters were recorded on Wednesday.

The downgrades followed an earlier full alert issued after the massive quake struck.