A strong earthquake measuring an estimated 6.1 in magnitude jolted eastern Japan early Friday, triggering emergency measures to check the state of railways, highways and nuclear plants.
There were no immediate reports of casualties and no tsunami warnings were issued, the Meteorological Agency said.
The temblor did not immediately affect the operation of nuclear power plants in Ibaraki and Fukushima prefectures, two of the most seriously affected areas, according to the Agency of Natural Resources and Energy.