Miyagi prefectural police said there were no immediate reports of damage from Friday's quake and tsunami, although traffic was being stopped in some places to check on roads.
Public television broadcaster NHK reported that five people were injured, including a 75-year-old woman in Miyagi who fell while fleeing the tsunami. Police said they could not immediately confirm those reports.
Shortly before the earthquake struck, NHK broke off regular programming to warn that a strong quake was due to hit. Afterward, the announcer repeatedly urged all near the coast to flee to higher ground.
The Meteorological Agency has an early warning system that, using data from seismographs scattered across Japan, enables it to provide advance warning of the estimated intensity and timing of a major quake. The warning for Friday's quake was issued six minutes before it struck, according to an unnamed official from the Meteorological Agency who spoke on national television more than an hour after the quake.
