Japan is poised to declare a toxic water leak at the Fukushima nuclear plant a level 3 "serious incident," its gravest warning since the massive 2011 earthquake and tsunami that sent three reactors into meltdown.
The country's Nuclear Regulation Authority said the leak was expected to be classified as a level 3 incident on the International Nuclear and Radiological Event Scale pending confirmation from the Vienna-based International Atomic Energy Agency.
"The current situation is at the point where more surveillance won't be enough to keep the accidents from happening," Shunichi Tanaka, chairman of the authority, said at a news conference Wednesday.
"Our job is now to lower the risk of these accidents from becoming fatal."
The leak previously had a level 1 "anomaly rating" on the scale, which ranges from zero, for no safety threat, to seven, for a major accident like the meltdowns at the plant after the earthquake and tsunami.
Tokyo Electric Power Company, or TEPCO, which is in charge of the plant, has struggled to manage the vast quantities of contaminated water at the plant since the tsunami, which swamped the facility.
Water pumped out of the stricken reactor buildings is being stored in large water towers at the site.
In response to the latest leakage of 300 tons of toxic water, a TEPCO spokesman said the company may finish removing radioactive water from a leaky tank to another tank at the plant by the end of Wednesday.
The leaky container is designed to hold as much as 1,000 tons of water, TEPCO said.
The International Atomic Energy Agency said it was aware of reports that the Nuclear Regulation Authority plans to rate the leak as a level 3 incident.
"The IAEA views this matter seriously and remains ready to provide assistance on request," the agency said.
Scientists have pointed to high radiation levels in the waters off the plant for more than a year as evidence of problems with the company's efforts to contain the water.
In July, TEPCO admitted that radioactive groundwater was leaking into the Pacific Ocean from the plant, even though an underground barrier was built to seal in the water, underscoring a growing sense of crisis at the site.
The authority said in a statement on its website that the plant "remains in an unstable condition, with various risks to be addressed, and in particular managing the issue of contaminated water as a high priority."
Michael Friedlander, a nuclear engineer and former U.S. power plant operator, said the level 3 classification was warranted for the type of situation faced by TEPCO, but he said the risk to the public outside the plant was very low.
"This is extremely radioactive water, and it would pose a very significant risk to the workers who are going to be in a position to clean it up," he told CNN.
"It's a very difficult situation because we don't know exactly know where the leak is coming from."
But TEPCO spokeswoman Mayumi Yoshida disputed Friedlander's assessment of the risk posed by the contaminated water. She said workers removing the water from the tank have sufficient protective clothing to prevent exposure.
Amid growing concerns this month about contaminated groundwater leaching into the ocean from the plant, Prime Minister Shinzo Abe ordered his government to find "multiple, speedy and sure" ways to stop the water's spread.
"We have to deal with this at a national level," he said.
But experts say that any potential solutions are likely to be difficult, technologically and politically.
Junko Ogura reported from Tokyo, and Katie Hunt reported and wrote from Hong Kong.