A tsunami about one metre high struck parts of the west coast along the Sea of Japan on Monday, with a larger wave expected, public broadcaster NHK reported.
The Japan Meteorological Agency has issued tsunami warnings for the coastal prefectures of Ishikawa, Niigata and Toyama.
Top government spokesperson Hayashi Yoshimasa told an emergency press conference authorities were still checking the extent of the damage and warned residents to prepare for possible further quakes.
Footage aired by NHK appeared to show buildings collapsing in Ishikawa, and tremors shook buildings in the capital Tokyo on the opposite coast.
More than 36,000 households lost power in Ishikawa and Toyama prefectures, utilities provider Hokuriku Electric Power said.
Japan's Nuclear Regulation Authority said no irregularities have been confirmed at nuclear power plants along the Sea of Japan, including five active reactors at Kansai Electric Power's Ohi and Takahama plants in Fukui Prefecture.
Hokuriku's Shika plant in Ishikawa, which was located the closest to the quake's epicentre, had already halted its two reactors before the quake for regular inspection and did no experience any impact from the quake, the agency said.
A huge earthquake and tsunami struck northeastern Japan on March 11, 2011, killing almost 20,000 people, devastating towns and triggering nuclear meltdowns in Fukushima.
