An earthquake measuring 8.0 in the Richter scale rocked Japan's northern island of Hokkaido on Friday morning.
Close to 180 people have been injured, 41,000 evacuated and 16,000 homes suffered a blackout.
The quake was followed by two strong aftershocks and several small tsunami waves.
Public broadcaster NHK reported that at least 187 people were hurt. Most of the injuries were caused by glass from shattered windows and falling objects in homes.
Officials said at least two people suffered serious injury, but most of the other injuries reported initially were minor.
A 61-year-old man cleaning up broken beer bottles on a street immediately after the quake was hit by an oncoming car and died, Hokkaido Police said. There were no reports of other quake-related deaths.
The quake struck at 450 am local time and was centred in the Pacific about 100 kilometers off Hokkaido's eastern shore. Japan's Central Meteorological Agency initially estimated the quake's magnitude at 7.8, but later revised that to 8.0.
That would make it the most powerful to hit anywhere in the world this year.
A powerful aftershock of magnitude 7.0 followed shortly after 6 am, and another hit at about 8 am.
The government warned residents to avoid coastal areas due to the possibility of tsunami.
Japan's meteorological agency said a tsunami of about 1.30 metres had struck Kushiro, a city of about 200,000 which appeared to be the worst hit. There were no immediate reports of damage from the wave.
Agencies
Earlier Report: Powerful quakes hit northern Japan
