Japanese nuclear regulators have raised the safety alert level of a radioactive water leak at the Fukushima nuclear power plant, saying it is now a "serious incident."
Operators of the crippled power plant said last week that 300 tons of contaminated water leaked out of a storage tank and that some may have reached the nearby ocean.
The leak was originally categorized as a Level One incident on an international scale. But regulators warned last week it would likely be upgraded to a Level Three case following meetings with U.N. nuclear officials.
The Fukushima plant suffered three reactor meltdowns after it was hit by a massive earthquake and tsunami in March 2011. Since then, it has tried to cool the reactors by pouring water over them.
But TEPCO, the plant's operator, has struggled to store the massive amounts of resulting contaminated water. Several leaks have been reported by TEPCO, which has acknowledged that some of the water seeped into the Pacific.
The problems have prompted the Japanese government to step up its efforts to clean up the plant.