Tokyo: A powerful aftershock that rocked an area of Japan has killed two people and injured around 100, emergency services said on Friday.

The Fire and Disaster Management Agency said a 63-year-old woman in Yamagata prefecture died after her respirator failed when the power was knocked out by the 7.1 magnitude tremor.

"Her respiratory equipment was found turned off. We believe the machine was turned off due to the (power) outage," a spokesman said.

The agency said one person also died in Miyagi prefecture -- the area worst hit by the 9.0 magnitude quake of March 11 and the tsunami it spawned.

Broadcaster NHK identified the Miyagi casualty as a 79-year-old man. It said he was found unconscious after the quake and taken to hospital, where he was confirmed dead.

The disaster management agency said at least 93 people were confirmed injured as of 9:30 am (0600IST) while Jiji Press said about 130 were injured.

Power remains off for about 3.6 million households in the northeastern region, Jiji said.