The Nuclear Regulation Authority said it was monitoring the situation closely at four nuclear power stations, after calling a special meeting of its commissioners.

Sensitivity over atomic power is high in Japan after the Fukushima disaster of 2011 was sparked by an earthquake and tsunami.

There was no safety issues at the Sendai nuclear station, which has two reactors and is about 120 kilometres (72 miles) south-southwest of Kumamoto city, close to where the quakes struck, NRA Chairman Shunichi Tanaka said at a press conference after the meeting.

The NRA is monitoring Genkai, about 100 kilometres northwest of Kumamoto, and Ikata, about 160 kilometres east-northeast of the quake zone.

Sendai and Genkai, which has four reactors, are operated by Kyushu Electric Power, while Ikata is owned by Shikoku Electric Power.

The regulator is also monitoring Shimane, a two-reactor station operated by Chugoku Electric Power, located further away on the main island of Honshu.

The country has been taking steps back to nuclear energy since the Fukushima disaster led to the eventual shutdown of all reactors. It turned on the first reactor at Sendai in August after a two-year blackout and the second at the same station in October.

Another station that began operating later, however, was shut down by a court last month.

Prime Minister Shinzo Abe and many in industry say nuclear power is necessary to cut fuel bills despite widespread public opposition to atomic power, even after electricity bills rose. (The Hindu)