Japan's nuclear regulator said on Wednesday (August 28) it has officially raised the severity rating of the latest radioactive water leak at the crippled Fukushima nuclear plant to Level 3 on an international scale for radiological releases.

The chairman of Japan's Nuclear Regulation Authority (NRA) formally announced the rating while adding that the situation remained unclear.

The upgrade by Japan's Nuclear Regulation Authority (NRA) raises the rating of what was Japan's first warning on the International Nuclear and Radiological Event Scale (INES) since the three reactor meltdowns at the Fukushima plant in March 2011, which were triggered by a massive earthquake and tsunami. Those meltdowns were classified as Level 7, the highest INES rating.

NRA which has complained about the data provided by the plant's operator, Tepco, said it had asked for more concrete assurances.

Tepco said last week that 300 tonnes of highly radioactive water leaked from a storage tank at the facility. The utility still does not know how long the water may have been leaking and said it was possible the contaminated water may have reached the Pacific Ocean.

Presented by Adam Justice