Tokyo/Fukushima: Japanese authorities on Sunday detected radioactivity 10 million times higher than normal in water in one of the six reactors at the crippled Fukushima nuclear plant forcing evacuation of workers, as the government warned that the crisis can aggravate.

The plant's operator, Tokyo Electric Power Company (TEPCO), said the radioactive materials tested 10 million times more than the usual level in water at the No 2 reactor complex, over two weeks after the devastating magnitude-9 quake and tsunami that struck Japan.

The level of contamination is about 1,000 times that of the leaked water already found in the basements of the Number 1 and 3 reactor turbine buildings, it said.

TEPCO said the radioactive materials in water of the No.2 reactor included 2.9-billion becquerels of iodine-134, 13-million becquerels of iodine-131, and 2.3-million becquerels each for cesium 134 and 137. These substances are emitted during nuclear fission inside a reactor core.

Emergency workers trying to cool the nuclear plant were temporarily evacuated following the detection of extremely high radiation.

Three workers at the No.3 reactor's turbine building were earlier exposed to the water containing radioactive materials 10,000 times the normal level on March 24.

As Japan battled to stabilise the nuclear plant, Chief Cabinet Secretary Yukio Edano conceded that the progress was slow.

Radiation levels 40 per cent higher than the yearly limit for the general public were also detected more than 30 km from the Fukushima power plant.

Earlier, Japan's nuclear agency had said that levels of radioactive iodine in the sea near the plant had risen to 1,850 times the normal level.

The Vienna-based International Atomic Energy Agency of the UN has also warned that Japan's nuclear crisis could go on for months.

According to Japanese police, 10,489 people were confirmed dead and more than 16,600 were missing after the March 11 earthquake and tsunami. A total of 6,333 dead were counted in Miyagi Prefecture, while in Iwate Prefecture 3,152 people had been killed. In Fukushima Prefecture, 946 people died.