As many as six tons of radioactive water has leaked into the ground at Japan’s Fukushima nuclear power plant, the Tokyo Electric Power Company said this week.  

Crews were transporting the water to storage tanks when it leaked from pipes at the plant's reactor building number one Wednesday.  

The water had been scrubbed in an advanced liquid processing system, the Japan Times reported, citing TEPCo. It seeped into the ground, officials said, and did not flow into the sea because there was no nearby drainage ditch.

The advanced liquid processing system can remove all radioactive substances except tritium--a radioactive isotope of hydrogen. It wasn’t clear how dangerous the water was before the spill.

Any spill or leakage at Fukushima causes heightened concern since an earthquake created tsunami waves that disabled the plant’s electrical and cooling systems, causing a meltdown and explosions that sent debris and radiation into the environment in March 2011.  More than 100,000 people were evacuated from their homes to ensure their safety after the disaster.

Wednesday’s leak occurred on the same day a team of experts from South Korea spent three hours at the plant, looking into the safety of Japanese fishery products.  The group was informed of measures to keep the nuclear crisis under control, but apparently were not made aware of the leak, the Times reported.  

The team inquired about the types of radioactive materials in the water and the results of radiation checks on local seawater, according to Japan's Fisheries Agency.

In September last year, South Korea banned imports of fishery products from Fukushima and seven other areas due to recurring water leaks at the Fukushima plant.