Tokyo Electric Power Company (Tepco) reported that the incident was caused by leaks in a contaminated water treatment device at the Fukushima Daiichi nuclear power plant, affected by a tsunami.

The leak was approximately 5.5 metric tons of water containing 22 billion bequerels (unit of measurement of radioactive activity) and some of the liquid may have flooded the ground at the site; however, the environment outside the plant had not been affected, the company said.

No significant changes have been detected in the control posts around the plant or in the measurements of the water monitors in the gutters inside the plant, the report added.

According to Tepco, the leak was discovered by plant workers shortly after 8:50 a.m., local time, on Wednesday.

The Fukushima nuclear power plant was damaged by a powerful earthquake and tsunami in 2011.

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