The United Nations atomic agency reported that the 7.1-magnitude earthquake in Japan Thursday did not change the status of the damaged Fukushima Daiichi nuclear power plant, but the temblor caused interruption of the power supply to a different nuclear plant and a uranium enrichment facility.

"NISA [Japan Nuclear and Industrial Safety Agency] confirms that no changes have been observed at the on-site radiation monitoring posts" at Fukushima Daiichi, the UN International Atomic Energy Agency (IAEA) said in an update following today's quake.

"The injection of [cooling] water into the reactor pressure vessels of Units 1, 2 and 3 was not interrupted," the agency added.

The epicentre of the earthquake was 20 kilometres from the Onagawa nuclear power plant and about 120 kilometres from the Fukushima Daiichi and Daini nuclear power plants, according to IAEA.

Today's temblor caused power loss on two of three lines supplying off-site power to the Onagawa nuclear power site. "Cooling of the spent fuel pool was temporarily lost, but has subsequently been restored," the agency reported, adding that no change was observed in the readings from the on-site radiation monitoring post. The status of the plant is currently being checked.

At the time of today's earthquake, unit 1 and 2 at the Tomari nuclear power plant in Hokkaido were in operation. The Hokkaido Electric Power Company reduced the generating power to 90 per cent of the generation capacity.

IAEA also quoted NISA as confirming that the earthquake caused Rokkasho reprocessing plant and uranium enrichment facility to lose off-site power, but emergency power supply kicked in.

The situation at the Fukushima Daiichi nuclear power plant remains "very serious," according to IAEA. The plant suffered major damage from the earthquake and tsunami that struck the country on 11 March and has been spewing radioactive contamination into the environment ever since.