The operator of Japan's stricken Fukushima nuclear power plant has suspended an operation to clean up radioactive water only hours after it had begun as radiation levels rose faster than expected.
The plan had got under way on Friday after being delayed by a series of glitches.
"The level of radiation at a machine to absorb caesium has risen faster than our initial projections," a spokesman for Tokyo Electric Power Company (TEPCO), said on Saturday.
"At the moment, we haven't specified the reason so we can't say when we can resume the operation. But I'd say it's not something that would take weeks."
The official said teams working at the plant believed the radiation rise could be linked to sludge flowing into the machinery intended to absorb ceasium. Another cause could be pipes surrounding it.
A resumption, the official said, was critical to deal with the highly radioactive water is stored there.
"Unless we can resume the operation within a week, we will have problems in disposing of the contaminated water," the official said.
"But if this is caused by the reasons we are thinking, we can resume the operation within a week."
The official said TEPCO foresaw no delay in its overall plan to bring the Fukushima Daiichi plant fully under control by the end of the year. The plan calls for a shutdown of its three unstable reactors by January 2012.
Officials had said earlier this week that large and growing pools of radioactive water at the Fukushima Daiichi plant were in danger of spilling into the sea within a week unless action was taken quickly.
Al Jazeera's Marga Ortigas, reporting from Tokyo, said that massive amounts of water were pumped in to cool three reactors at the plant.
"The problem is that there is too much water in the plant already," Ortigas said. "The last thing they want to do right now is get more contaminated water into the sea."
Around 110,000 tonnes of highly radioactive water is stored at the plant.
Some scientific experts believe that the nuclear disaster is to be far worse than governments are revealing to the public.
"Fukushima is the biggest industrial catastrophe in the history of mankind," Arnold Gundersen, a former nuclear industry senior vice-president, told Al Jazeera.
"Fukushima has three nuclear reactors exposed and four fuel cores exposed.
"You probably have the equivalent of 20 nuclear reactor cores because of the fuel cores, and they are all in desperate need of being cooled, and there is no means to cool them effectively."
TEPCO has been spraying water on several of the reactors and fuel cores, generating hundreds of thousands of tons of highly radioactive sea water that has to be disposed of.
"They are pouring in water and the question is what are they going to do with the waste that comes out of that system, because it is going to contain plutonium and uranium," Gundersen said.
"Where do you put the water?"
The March 11 tsunami and earthquake knocked out cooling systems and emergency backup generators at the Fukushima plant, leading to meltdowns and radiation leaks in the worst nuclear disaster since Chernobyl in 1986.
The Fukushima crisis shattered Japan's confidence in the safety of nuclear energy and has prompted anti-nuclear sentiment.
But there are also concerns that Japan will face a serious summertime power crunch unless more of its reactors get back on line.