Japan appeared resigned on Monday to a long fight to contain the world's worst atomic crisis in 25 years after high radiation levels complicated work at its crippled nuclear plant. Engineers have been battling to control the six-reactor Fukushima complex since it was damaged by a March 11 earthquake and tsunami that also left more than 27,000 people dead or missing across Japan's devastated north east.
-- Radiation levels highest since crisis began on March 11
-- Battle to control Fukushima plant seen far from over
Radiation at the plant has soared in recent days: latest readings at the weekend showed contamination 100,000 times normal in water at reactor No 2 and 1,850 times normal in the nearby sea.
Those were the most alarming levels since the crisis began, experts said.
Under-pressure plant operator Tokyo Electric Power Co (TEPCO) conceded what experts have long been saying: that Japan now faces a protracted and uncertain operation to contain overheating fuel rods and prevent a meltdown.
"Regrettably, we don't have a concrete schedule at the moment to enable us to say in how many months or years (the crisis will be over)," TEPCO vice-president Sakae Muto said in the latest of round-the-clock briefings the company holds.
Though experts said radiation in the Pacific waters will quickly dissipate, the levels at the site are clearly dangerous, and the 450 or so engineers there have won admiration and sympathy around the world for their bravery and sense of duty.
The nuclear crisis is an especially sensitive subject for Japanese given they are the only nation to have been hit by atomic bombs, at Hiroshima and Nagasaki in 1945.
Last week, three workers at Fukushima were hurt with radiation burns to their legs after water seeped over their boots, and on Sunday engineers had to abandon reactor No 2 after the new reading.
Further afield, beyond the evacuation zone around Fukushima, there has been plenty of evidence of radiation - from tap water in Tokyo 240 km (150 miles) south of the nuclear facility to particles found as far away as Iceland.
Japanese officials and international nuclear experts have generally said the levels away from the plant are not dangerous for humans, who anyway face comparable radiation doses on a daily basis from natural substances, X-rays or plane flights.
A clutch of nations including the United States have banned imports of food from the areas closest to the Fukushima plant.
Two of the plant's six reactors are now seen as safe but the other four are volatile, occasionally emitting steam and smoke.
TEPCO officials indicated the highly contaminated water is probably coming from inside the reactors rather than from pools of spent fuel rods outside.
Experts are anxious to find out whether the reactor core is broken and leaking, as that could lead to a meltdown.
One long-term solution may be to entomb the Fukushima reactors in sand and concrete as happened at Chernobyl, Ukraine, after the 1986 disaster that was the world's worst. But there is too much heat for that to be considered yet, experts say.