The leak of radioactive water from the crippled Fukushima Daiichi nuclear power plant constitutes a Level 3 "serious incident" on the seven-step International Nuclear Event Scale, Japanese authorities said Wednesday.

Around 300 tons of highly radioactive water has escaped from a storage tank, according to Japan's Nuclear Regulation Agency, which cited the volume of the leak and the "fact that there is no safety protective layer remaining at the facility" as the reasons for raising the alert from Level 1.

The NRA said it plans to consult with the International Atomic Energy Agency on the next steps to take.

The Fukushima plant was devastated in March 11 by a massive earthquake and subsequent tsunami that disabled cooling systems and led to several meltdowns.

The crisis was serious enough to rate a Level 7 designation, a distinction the Fukushima disaster shares only with the 1986 meltdown of the Chernobyl plant in Ukraine.

Water escaping from the storage tank is so radioactive that one hour's worth of exposure would equal the maximum permissible exposure for a nuclear plant worker over five years.

Some of the radioactive water may have flowed into the Pacific Ocean, the plant's operator, Tokyo Electric Power Co, said Wednesday. EFE