Tokyo: Heavy rain on Monday pelted Japan`s northeast region which was devastated in the March 11 earthquake and tsunami, adding to radioactive contaminated water at the crippled Fukushima nuclear power plant.
A low-pressure system -- the remnant of Typhoon Songda -- hung over the Pacific coast and dumped up to 15 centimetres (six inches) of rain in 24 hours, the Japan Meteorological Agency said.
The level of water in the basement of one of the atomic plant`s six reactor buildings rose by nearly 20 centimetres (eight inches) in 24 hours by early Monday, the facility`s operator Tokyo Electric Power Co. (TEPCO) said.
"We presume the level of water has risen due to the rainwater which has seeped into the ground," TEPCO official Junichi Matsumoto said as the water in the number one reactor building reached 5.7 metres (19 feet).
Emergency workers have been pouring thousands of tonnes of water onto reactors and pools for storing spent fuel rods, to control overheating after cooling systems failed in the disaster.
TEPCO says that fuel rods are presumed to have melted in three reactors.
The cooling operations have left four reactor units with radioactive contaminated water pooling inside.