Operators of a nuclear power plant crippled by the Japanese earthquake and tsunami say highly radioactive water has been found outside one of the reactor buildings.
The Fukushima Daiichi plant was badly damaged after the 9.0-magnitude quake triggered a tsunami that devastated the country's north-east coast on 11 March.
The death toll has now passed 10,000 and more than 17,000 people are unaccounted for.
Engineers have been battling to cool the reactors and spent fuel ponds to avoid a large-scale release of radiation.
The BBC reports that water outside the reactor shows levels of radiation equivalent to the highest amounts discovered inside.
It was found in maintenance tunnels leading from the reactors which open into shafts much closer to the sea than the reactors.
The tunnel leading from reactor No 2 is showing the highest levels of radiation. According to the nuclear safety agency, contaminated water there has risen to within one metre of the top of the shaft.
However, the Tokyo Electric Power Company says there is no evidence at this stage that the water has reached the Pacific Ocean.
Meanwhile, France says it will send specialists in treating radioactive water to Japan after the plant's owner asked for help.
Interior Minister Eric Besson says France's leading nuclear group AREVA will send two specialists in the recuperation and treatment of radioactive water, AFP reports.
Mr Besson says the situation at Fukushima is "critical" and France is ready to send as many experts as necessary.
Plutonium in soil
Plutonium has been found in soil at the Fukushima plant, but the plant's operators say the levels do not pose a threat to human health.
A spokesperson for Tokyo Electric Power says they believe at least two of the five soil samples taken are directly linked to reactor problems at the plant.
The company says it will strengthen its monitoring system and will continue to study soil samples from the plant.
The United Nations nuclear energy agency has called for a summit to
improve disaster management following the crisis.