THE OPERATORS OF the troubled Fukushima I nuclear power plant have said that a reading taken at the plant this morning – which said the level of radioactivity in the water at one reactor unit at the plant was ten million times the allowed level – was an error.

The previous recording, taken by workers at reactor 2, had seen workers evacuated immediately before they had even had time to take a second recording, and had once again delayed efforts to control the leaking complex.

The air, meanwhile, measured 1,000 millisieverts per hour — four times the limit of 250 millisieverts deemed safe by the government, a spokesman for plant operator TEPCO told reporters.

Word of the startling jump in radioactivity in Unit 2 came as TEPCO struggled to pump the contaminated water from four troubled reactor units at the overheated Fukushima I plant, 250 kilometres north-east of Tokyo. The reading was so high that the worker measuring the levels fled before taking a second reading, officials said.

Japan’s Nuclear and Industrial Safety Agency had warned yesterday that radioactivity inside the units was rising fast and that extracting the radioactive water was a priority.

The discovery over the last three days of radioactive water in one or more units at the six-unit complex has been a major setback in the urgent mission to get the plant’s crucial cooling system back up and operating more than two weeks after a massive earthquake and tsunami.

Since the quake and tsunami, nuclear workers have raced to cool down the overheating plant as radiation made its way into food, seawater and even tap water supplies as far away as Tokyo.

Officials said the discovery Thursday of highly radioactive pools of water in Unit 3 led to suspicions that radiation was leaking due to a possible breach. Two workers were being treated at a hospital for possible burns sustained from wading into the contaminated water.

Chief Cabinet Secretary Yukio Edano said the exact source of the leak wasn’t clear yet but radioactive water is “almost certainly” seeping from a reactor core.

The magnitude-9 quake off Japan’s northeast coast March 11 triggered a tsunami that barreled onshore and disabled the Fukushima plant, complicating a humanitarian disaster that has killed more than 10,000 people and left hundreds of thousands homeless.

The official death toll stood at 10,489 on Sunday, with more than 16,620 people missing, police said. The final death toll was expected to top 18,000.

Additional reporting by AP

Video: Experts fear reactor core breached at Fukushima >