THE Japanese government withheld the release of data showing that levels of radiation more than 30 kilometers from the crippled Fukushima nuclear plant exceeded safe levels, broadcaster NHK reported Monday citing official documents.

The facility was rocked by a devastating earthquake and magnitude 9.0 tsunami which struck Japan's northeast coast on March 11. Radiation has since been seeping from the complex, with the government imposing a 20-kilometre evacuation zone.

Low levels of radioactive material have also been detected in other countries including the US and Britain.

Computer projections taken on March 16 showed that people from as far away as 30 kilometres from the nuclear plant would be exposed to more than 100 millisieverts of radiation if they were outdoors for 24 hours between March 12 and 24.

It also indicated that the radiation could spread northwest and southwest of the facility.

The normal level of background radiation people are exposed to in their daily lives without harm is about one to 1.5 millisieverts a year.

The Japanese government has defended its failure to release the data until March 23, saying the amount of radioactive leakage and the areas affected were not clear at the time.

Originally published as Japanese hid information on radiation