Japan's crippled nuclear plant has a new leak of highly radioactive water entering the Pacific Ocean after a storage tank overflowed.

Plant operator Tokyo Electric Power Co. said Thursday that workers detected the water dripping from the top of a tank when they were patrolling the site the night before.

TEPCO estimates 430 liters (110 gallons) of water leaked outside a concrete barrier surrounding the tank and four others. TEPCO believes the water reached the sea via a ditch next to the barrier.

Massive amounts of water have been used to cool the reactors and fuel rods since the March 2011 earthquake and tsunami destroyed the Fukushima Dai-ichi plant's cooling system. Leaks of the contaminated water are causing concerns over the plant's stability.