Japan to issue gravest warning since earthquake on Fukushima nuclear plant leaks

Local government officials and nuclear experts inspect the Fukushima Dai-ichi nuclear plant earlier this month.

STORY HIGHLIGHTS

• Japan poised to issue warning on Fukushima nuclear plant
• Toxic water leaks to be classified a level 3 serious incident
• Warning at highest level since 2011 earthquake and tsunami triggered meltdown
• The leak had previously been assigned a level 1 "anomaly rating"

Tokyo (CNN) -- Japan is poised to declare a toxic water leak at the Fukushima nuclear plant a level 3 "serious incident," its gravest warning since the aftermath of the massive 2011 earthquake and tsunami that sent three reactors into meltdown.

The country's Nuclear Regulation Authority (NRA) told CNN the leak was due to be formally classified as a level 3 incident on the International Nuclear and Radiological Event Scale after a meeting later Wednesday.

The leak had previously been assigned a level 1 "anomaly rating" on the scale, which ranges from zero, for no safety threat, to seven -- a major accident like the meltdowns that were seen at the plant in the wake of the massive 2011 earthquake and tsunami.

Tokyo Electric Power Company (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.

Scientists have pointed to high radiation levels in the waters off the plant for more than a year as evidence of an ongoing leak.

In July, TEPCO admitted that radioactive groundwater was leaching into the Pacific Ocean from the plant despite building an underground barrier to seal the water, underscoring a growing sense of crisis at the site.