Japanese authorities have warned that radiation levels around a leaking tank at the Fukushima nuclear plant are high enough to prove lethal within four hours of exposure.
The new readings are 18 times higher than originally thought and highlight the struggle to bring the leak under control more than two years after Japan's devastating earthquake crippled the plant.
The Tokyo Electric Power Company reported last week that radioactive water had leaked from a storage tank into the ground.
The company says radiation of 1800 millisieverts per hour - enough to kill an exposed person in four hours - was detected near the bottom of one storage tank on Saturday.
It says the radiation levels of the same tank ten days ago was 100 millisieverts per hour.
The new readings will have direct implications for the radiation doses received by workers who spent several days last week trying to stop the leak, the BBC reports.
The Fukushima plant was destroyed by a tsunami in March 2011 in the worst nuclear disaster since Chernobyl, a quarter of a century earlier.