TOKYO (Reuters) - 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.
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.
"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 cesium 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.
"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 Organization (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.
Japan is a net importer of food, but has substantial exports -- mainly fruit, vegetables, dairy products and seafood -- with its biggest markets in Hong Kong, China and the United States.
China said it is monitoring food imports from Japan but also took a swipe against panic by jailing a man for 10 days for spreading rumors about contamination of its waters.
State media said the computer company worker, who had urged people to avoid sea products for a year, was also fined 500 yuan ($76.13) and had confessed to "deep awareness of his mistake."
South Korea is expanding inspection of Japanese food.
And in Taiwan, one Japanese restaurant is offering diners a radiation gauge in case they are nervous about the food.
The United States said it was distributing potassium iodide to American personnel in Japan "out of an abundance of caution" should the radiation treatment be needed.
The prospects of a nuclear meltdown in the world's third-biggest economy - and its key position in global supply chains especially for the automobile and technology sectors - rattled investors worldwide last week and prompted rare joint currency intervention by the G7 group of rich nations.
Damage is estimated at around $250 billion, making it the world's costliest natural disaster.
Japan's economic growth is expected to depress in the first half before reconstruction kicks in.
Global stocks rose on Monday as risk appetite returned following progress in the nuclear crisis. The yen slid on speculation of more Group of Seven intervention.
In a symbolic boost for Japan, billionaire investor Warren Buffett said the quake and tsunami were an "enormous blow" but also presented a "buying opportunity" given recovery prospects.
The official death toll - 8,805 by Tuesday morning - is certain to keep rising, with another 12,654 reported missing.
Police say more than 15,000 people probably died in Miyagi prefecture, one of four that took the brunt of the tsunami.
The 9.0-magnitude quake and ensuing 10-meter (32-ft) tsunami obliterated towns, which are now wastelands of mud and debris, leaving more than 350,000 people homeless.
Japanese are famed for resilience though, and there was none of the chaos or looting that major global disasters often spark.
In one devastated northern town, Rikuzentakata, rebuilding has even begun to help families living on mats in cramped shelters, separated from neighbors only by cardboard.
Steel structures, with walls and wood floors, have been erected at a hilltop school, to provide temporary housing.
Nearly 9.5 million foreigners visited Japan last year.
But, like Korean housewife Jin Hye-ryun who canceled a planned visit in May, many tourists are re-thinking.
"Safety is not guaranteed," she said. "Besides, think about people dying there. No one wants to go there to have fun."
There is widespread admiration for the workers facing high radiation dosages on the front line at Fukushima. Some have wept with tension and relief after finishing their shifts.
Other tales of heroism and horror abound, including a fire chief traumatized after sending a team to close a faulty sea-wall manually just as the tsunami struck, killing them all.
As well as hunting for bodies and survivors, rescuers have been painstakingly recovering photographs and other mementos from the wreckage and laying them out for possible collection.
Additional reporting by Paul Eckert and James Topham in Tokyo; Yoko Kubota and Chang-ran Kim in Rikuzentakata; Jon Herskovitz and Chisa Fujioka in Kamaishi; Sui-Lee Wee in Beijing; Jungyoun Park in Seoul; Alister Doyle in Oslo; Writing by Andrew Cawthorne and Jason Szep; Editing by Miral Fahmy