Japan has declared a nuclear emergency after the operator of Fukushima No.1 nuclear plant reported an abnormality today, following a major earthquake, the industry ministry has announced.

No radioactive leakage has been reported so far, but it has been confirmed that the nuclear plant, operated by Tokyo Electric Power Company, has not gone to plan, Kyodo new reports.

The system to cool reactor cores stopped at No.1 and No.2 reactors at the plant.

The 8.9 magnitude earthquake hit the country at 3.15pm local time, causing a 10m tsunami to sweep away everything in its path.

At least 20 people have been killed.