Authorities say a strong aftershock that hit Japan's tsunami-battered northeast has killed two people and injured dozens more.

A 7.1-magnitude earthquake struck late Thursday, the strongest aftershock since a massive quake and tsunami pulverized hundreds of kilometres of the northeastern coast.

Fire department spokesman Junichi Sawada said Friday two people were killed. A 79-year-old man died of shock. A woman in her 60s was killed when her oxygen tank failed because of power outages.

The national police agency says 132 people have been injured.

The quake was centered in roughly the same area as the March 11 9.0-magnitude tremor.