Radiation levels around Japan's Fukushima nuclear plant are 18 times higher than previously thought, Japanese authorities have warned.
Last week the plant's operator reported radioactive water had leaked from a storage tank into the ground.
It now says readings taken near the leaking tank on Saturday showed radiation was high enough to prove lethal within four hours of exposure.
The plant was crippled by the 2011 earthquake and tsunami.
The Tokyo Electric Power Company (Tepco) had originally said the radiation emitted by the leaking water was around 100 millisieverts an hour.
However, the company said the equipment used to make that recording could only read measurements of up to 100 millisieverts.
The new recording, using a more sensitive device, showed a level of 1,800 millisieverts an hour.
The new reading will have direct implications for radiation doses received by workers who spent several days trying to stop the leak last week, the BBC's Rupert Wingfield-Hayes reports from Tokyo.
In addition, Tepco says it has discovered a leak on another pipe emitting radiation levels of 230 millisieverts an hour.
Yeah, this seems like a bad thing. Fukushima is leaking, containment has completely failed, and radioactive material has been getting into the ocean for two years now. There doesn't seem to be any way to slow it down. either. This stuff could burn for decades, guys. By then, the damage to the Pacific rim is going to be devastating, not to mention to Japan itself.
The plant is just as lethal now as it was in 2011. That's horrifying, but not shocking. We'll keep up with this story as we have for the last 30 months.