Japanese engineers on Monday were forced to release radioactive water into the sea while resorting to desperate measures such as using bath salts to try to find the source of the leaks at a crippled nuclear power complex.
Engineers also planned to build a giant silt curtain in the ocean to stop the spread of more contamination from the Fukushima Daiichi plant.
The plant operator had to release low-level radioactive seawater that had been used to cool overheated fuel rods after it ran out of storage capacity for more highly contaminated water, Chief Cabinet Secretary Yukio Edano said.
Operator Tokyo Electric Power (TEPCO) said it would release over 10,000 tonnes of contaminated water that was about 100 times more radioactive than legal limits.
Engineers are still struggling to regain control of damaged reactors at the plant in the worst nuclear crisis since Chernobyl in 1986, with the government urging TEPCO to act faster to stop radiation spreading.
But it could take months to stem the leaks, warned one official, and even longer to regain control of the power station, damaged by a March 11 earthquake and tsunami.
"We need to stop the spread of (contaminated water) into the ocean as soon as possible. With that strong determination, we are asking Tokyo Electric Power Co to act quickly," said Edano.
"If the current situation continues for a long time, accumulating more radioactive substances, it will have a huge impact on the ocean."
In the face of Japan's biggest crisis since World War Two, one newspaper poll said nearly two-thirds of voters wanted the government to form a coalition with the major opposition party and work together to recover from the natural disaster.
Underlining the concern over the impact on the world's third largest economy, a central bank survey showed big manufacturers expected business conditions to worsen significantly in the next three months, although they were not quite as pessimistic as some analysts had expected.
An aide to embattled Prime Minister Naoto Kan said on Sunday the situation at the Fukushima plant, 240 km (150 miles) north of Tokyo, had "somewhat stabilised", but it may take months to stop radiation leaks.
At least four of the plant's six reactors will be scrapped once brought under control, but that could take decades.
BATH SALTS, SEA CURTAIN
In their desperation, TEPCO engineers have used anything at hand to try to stop the leaks.
At the weekend, they mixed sawdust and newspapers with polymers and cement in an unsuccessful attempt to seal a crack in a concrete pit at reactor No.2.
On Monday, they resorted to powdered bath salts to produce a milky colour to help trace the source of the radiation leak.
TEPCO said it was also planning to drape a curtain into the sea off the nuclear plant to try to prevent radioactive silt drifting out into the ocean.
The silt-blocking fence will take several days to prepare, said Hidehiko Nishiyama, deputy director-general of the Nuclear and Industrial Safety Agency (NISA).
The exact source of the radiation leaks remains a mystery, with NISA investigating a damaged embankment near a sluice gate at the No.2 reactor and the possibility it may be seeping through a layer of small stones below a concrete pipe.
PM UNDER PRESSURE
The 9.0 magnitude quake and tsunami left nearly 28,000 people dead or missing and Japan's northeast coast a splintered wreck. The world's costliest natural disaster has hit economic production and left a damages bill which may top $300 billion.
"The damage from the nuclear crisis and the subsequent power shortage will last for several years," said Eiji Hirano, former assistant governor of the Bank of Japan.
"There's a strong chance Japan's economy will contract in the current fiscal year," he told Reuters in an interview.
After three weeks, many Japanese are angry the humanitarian disaster seems to have taken a back seat to the nuclear crisis.
More than 163,710 people are living in shelters, with more than 70,000 people evacuated from a 20 km (12 mile) no-go zone around the nuclear plant. Another 136,000 people living a further 10 km out have been told to leave or stay indoors.
Though criticised for his crisis management, voter support for Kan's government rose to 31 percent in a Yomiuri newspaper poll, from 24 percent in a survey conducted before the quake. Almost 70 percent of respondents, however, believed Kan was not exercising leadership, with 19 percent wanting him to step down.
There has been talk that Kan's Democratic Party of Japan should join forces with its main political opponent, the Liberal Democratic Party (LDP).
But there has been no sign the two are close to any deal. Kan last month invited the head of the LDP to join the cabinet as deputy premier for disaster relief, but he declined.
YEARS OF ECONOMIC RECOVERY
Japan, one of the world's most indebted nations, faces years of recovery from the disaster and the government will need to tread carefully not to further damage the economy, said Hirano.
"What's different this time from the time of the Kobe quake (1995) is that Japan's fiscal state is much worse. The government faces the difficult task of trying to come up with funds for disaster relief without triggering a big disruption in markets," he said.
"I don't think the government will resort to big fiscal spending relying heavily on huge bond issuance. But if it does, there's a risk it will severely undermine market confidence ... That will hurt Japan's economy seriously."
Manufacturing has already slumped to a two-year low as a result of power outages and quake damage hitting supply chains and production.