TOKYO - Global anxiety rose over radiation from Japan's crippled nuclear plant even as engineers won ground in their battle to avert disaster from the world's worst atomic crisis since Chernobyl.

Kazumi Sato, from Soma in Fukushima, undergoes a screening test for signs of nuclear radiation by a doctor at a welfare center in Yonezawa, northern Japan, 98 km (61 miles) from the Fukushima nuclear plant, March 21, 2011. Sato did not show harmful levels of radiation. [Photo/Agencies]

The high-stakes drama at the battered Fukushima nuclear power complex is playing out while the Asian nation grapples with the aftermath of the March 11 earthquake and tsunami that left at least 21,000 people dead or missing.

Technicians working inside an evacuation zone round the stricken plant on Japan's northeast Pacific coast have managed to attach power cables to all six reactors and started a pump at one of them to cool overheating nuclear fuel rods.

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"We see a light for getting out of the crisis," an official quoted Prime Minister Naoto Kan as saying, allowing himself some rare optimism in Japan's toughest moment since World War II.

Yet away from the plant, mounting evidence of radiation in vegetables, water and milk spread jitters among Japanese and abroad despite officials' assurances levels were not dangerous.

Plant operator Tokyo Electric Power Company said radiation was found in the Pacific nearby, not surprising given rain and the hosing of reactors with sea-water.

Radioactive iodine in the sea samples was 126.7 times the allowed limit, while caesium was 24.8 times over, Kyodo news agency said. That still posed no immediate danger, TEPCO said.

"It would have to be drunk for a whole year in order to accumulate to one millisievert," a TEPCO official said, referring to the standard radiation measurement unit. People are generally exposed to about 1 to 10 millisieverts each year from background radiation caused by substances in the air and soil.

Japan has urged some residents near the plant to stop drinking tap water after high levels of radioactive iodine were detected. It has also stopped shipments of milk, spinach and another local vegetable called kakina from the area.

"What I want the people to understand is that their levels are not high enough to affect humans," Chief Cabinet Secretary Yukio Edano said.  

Experts say readings are much lower than around Chernobyl after the 1986 accident in Ukraine. Some warned against panic.

Apples with "Produced in Japan" stickers are seen at a Japanese supermarket in Hong Kong March 21, 2011. The World Health Organization said on Monday that the detection of radiation in food after an earthquake damaged a Japanese nuclear plant was a more serious problem than it had first expected. [Photo/Agencies]

"You would have to eat or drink an awful lot to get any level of radiation that would be harmful," said British nuclear expert Laurence Williams.

"We live in a radioactive world: we get radiation from the earth, from the food we eat. It's an emotive subject and the nuclear industry and governments have got to do a lot more to educate people."

The World Health Organisation (WHO) said the radiation impact was, however, becoming more serious than first thought, when it was expected to be limited to 20-30 km from the plant.

However, Peter Cordingley, spokesman for the WHO's regional office, told Reuters there was no evidence of contaminated food reaching other countries from the Fukushima complex, which lies 240 km (150 miles) north of Tokyo.

In the city of 13 million, many residents remain indoors or wear masks when out in the street.  Some expatriates and locals left after the accident.