The operator of Japan's stricken Fukushima nuclear plant said on Sunday it had found highly radioactive water dripping from a pipe connecting two coolant tanks at one of four radiation hotspots.
The discovery came hours after Tokyo Electric Power Co (TEPCO) said late on Saturday that radioactivity at one of the other four sites measured 1,800 millisieverts per hour - a dose that would kill a human left exposed to it in four hours.
The reading was 18 times higher than a recording at the same place taken on August 22, though the company said the first measurement was done with equipment that could only reach up to 100 millisieverts.
A TEPCO spokesman said the radiation of 1,800 millisieverts was largely beta ray with weak penetration force, which workers can easily block by wearing protection jackets.
TEPCO has long struggled to deal with the huge amounts of water used to cool reactors that went into meltdown after being struck by an earthquake and tsunami in 2011.
The government has promised to get more involved in the plant's clean-up after TEPCO's efforts came in for fierce criticism.
The leaking pipe was found to be dripping one drop about every 90 seconds, the company said.
Workers tightened 12 bolts to stop the leak and bolstered the repair using special material and plastic tape.
Water with a radioactivity of 230 millisieverts per hour was found below it, the operator said, while at two other hotspots near tanks workers also measured radioactivity of 70 and 220 millisieverts per hour. The fourth hotspot measured 1,800.
Two of the sites, including where the pipe was dripping, were completely new discoveries, while at the other two sites the readings were considerably higher than previously measured.
"We have to suspect that the high radiation levels were detected due to the toxic water oozing out of the flange connections," the spokesman said, adding the company has not yet come to a conclusion.
Last week the plant operator admitted that 300 tonnes of toxic water had leaked from one large tank - one of around 1,000 on the site - before anyone had noticed.
The spill sparked fears the toxic water may have seeped into the ocean. It was categorised as a Level 3 event, the most serious category since the meltdown itself.
In response to growing domestic and international criticism of TEPCO's handling of the crisis, Prime Minister Shinzo Abe on Thursday promised the world his government would play a greater role in stopping leaks of highly radioactive water.
"The accident in Fukushima cannot be left entirely to Tokyo Electric Power. There is a need for the government to play a role with a sense of urgency, including taking measures to deal with the waste water," he said.
Abe's pledge came as the world's nuclear watchdog urged Japan to explain more clearly what was happening at Fukushima and avoid sending "confusing messages" about the disaster.