Tokyo (CNN) -- Authorities on Friday blamed three deaths and more than 140 injuries on a fresh earthquake that struck northern Japan a day earlier, shaking up a region already devastated by March's historic temblor.
The dead included an 85-year-old man who collapsed and died while trying to get to a shelter with his family and a 79-year-old man who was reported dead on arrival at the Red Cross hospital in the coastal city of Ishinomaki, doctors there reported.
Further inland, in Yamagata Prefecture, a 63-year-old woman died after a power outage caused by the quake stopped her oxygen, the prefecture's government told CNN.
Another 132 people were injured, 17 of them seriously, according to Japan's National Police Agency.
"It's been a while since the big earthquake so I had started to feel secure again," said Yusuaki Nomura, standing in line outside a supermarket in Kitakami, an inland city in Itake Prefecture. "There will certainly be another big aftershock and I realize I should get ready for the next one and be more prepared."
The Japan Meteorological Agency initially rated the Thursday quake a magnitude 7.4, then lowered its estimate to 7.1 -- the same figure the U.S. Geological Survey recorded. It was considered an aftershock from the magnitude 9 quake and tsunami that struck nearby March 11, leaving more than 12,700 dead and 14,700 missing to date.
The Geological Survey said the quake was centered 66 kilometers (41 miles) from Sendai, one of the areas worst hit by last month's 9.0-magnitude quake, and 333 kilometers (207 miles) from Tokyo. It caused noticeable shaking in the capital for about a minute.
The new quake struck shortly after 11:30 p.m. Thursday (10:30 a.m. ET), closer to the coast than the March 11 disaster. It triggered a tsunami warning for one section of the coast and advisories for others, but the advisories were lifted about 90 minutes later.
"I was terrified, then all the lights went off and it was pitch black, which was even more scary," said Chieko Watanabe, a Kitame resident as she stood outside a hardware store which had run out of generators and batteries.
Japanese nuclear regulators said no additional damage was reported at the Fukushima Daiichi nuclear power plant, where workers have been battling to keep overheating reactors under control since the March 11 quake. Workers evacuated the plant when the quake hit, but water continued flowing into the reactors, the Tokyo Electric Power Company told reporters.
But at the Onagawa nuclear plant, about 140 kilometers (88 miles) to the north, the latest rumbles caused several small leaks of radioactive water that totaled about 15 liters (3.9 gallons), the Sendai-based Tohoku Electric Company reported.
The leaks came from pools housing spent fuel from the plant's three reactors, which have been shut down since the March 11 earthquake, Tohoku Electric said. Their radioactivity was far below the threshold that posed a threat to human health, according to data released by the company.
A handful of roads were damaged as well as a few homes. About 3.9 million homes remained without power, police said, and water and train services were disrupted in some places.
A Japanese researcher said Friday that residents in eastern Japan, including Tokyo, can expect more such aftershocks in the coming months.
"We should not be surprised to have magnitude-7 level aftershocks even a year afterward anywhere as wide as east Japan in the wake of such mega-quake of magnitude 9," said Satoko Oki of the Earthquake Research Institute of Tokyo University.
CNN's Kyung Lah, Yoko Wakatsuki and Noriaki Kawai contributed to this report.