Nuclear regulators in Japan say the crippled Fukushima nuclear power plant is facing a new emergency caused by a build-up of radioactive groundwater.
The Nuclear Regulatory Authority said on Monday that a barrier built to contain the water has already been breached.
It said this means the amount of contaminated water seeping into the Pacific Ocean could accelerate rapidly.
There has been a spate of water leaks and power failures at the plant since the earthquake and tsunami in 2011.
Tokyo Electric Power Company admitted for the first time last month that radioactive groundwater had breached an underground barrier and been leaking into the sea, but said it was taking steps to prevent it.
The Asahi newspaper predicted on Saturday contaminated water could rise to the ground's surface within three weeks.
The BBC reports the contaminated water is thought to have come from the 400 tonnes of groundwater pumped into the plant every day to cool the reactors.
TEPCO admitted on Friday that a cumulative 20 trillion to 40 trillion becquerels of radioactive tritium may have leaked into the sea since the disaster.
A BBC correspondent said the only course of actionis to pump water out. But this has to be stored, and more than 1000 giant holding tanks surrounding the plant are nearly all full.
TEPCO said on Monday it plans to start pumping out a further 100 tonnes of groundwater per day.