A strong aftershock rattled northeastern Japan on Monday, briefly knocking out the power supply at the crippled Fukushima Daiichi nuclear plant.

Japan’s nuclear safety agency said that power was resumed to the unit 1, unit 2 and unit 3 reactors after a 50-minute interruption, allowing the critical cooling of hot fuel rods to resume. The temporary outage did not appear to have any safety implications, an official from Japan’s Nuclear and Industrial Safety Agency said.

The 6.6-magnitude aftershock, centered 50 miles south of Fukushima, came exactly one month after a 9.0 quake rocked Japan’s coastline and delivered a massive tsunami wave. The double disaster killed tens of thousands and knocked out central and backup power at the Daiichi facility, triggering a nuclear emergency that workers are still trying to control.

On Monday, the government pushed to enlarge its 12-mile evacuation radius around the crippled plant, adding to the scores of thousands of Japanese already pushed from their homes. Though government spokesman Yukio Edano said the risks of a widespread radiation leak had become “considerably lower,” he said that certain areas within 12 to 19 miles of the plant, based on radiation readings, will be given mandatory evacuation orders.

Monday’s aftershock, which struck at 5:16 p.m. local time, rattled buildings in Tokyo, 100 miles southwest of the epicenter. It followed a major 7.1-magnitude aftershock four days earlier that injured hundreds, killed at least two and briefly interrupted power supply at two nuclear plants — though not at Daiichi.

After Monday’s aftershock, no abnormal radiation readings were reported at other nuclear plants. A tsunami warning was issued but soon called off.

Power was out in more than 200,000 homes in the region closest to the temblor, and television cameras showed at least one major landslide that submerged a car, prompting attention from rescue crews.