By Mayumi Negishi and Kazunori Takada
TOKYO (Reuters) - Japan said on Friday that workers who suffered burns while trying to cool a crippled reactor were exposed to radiation levels 10,000 times higher than expected, adding evidence that the crucial containment vessel for nuclear fuel had been ruptured.
That could mean a serious reversal after days of apparently steady progress in containing radiation leaks after a killer earthquake and tsunami tore through the Fukushima complex north of Tokyo two weeks ago.
More than 700 engineers have been working in shifts around the clock to stabilize the six-reactor Fukushima complex but they pulled out of some parts when three workers replacing a cable at the No. 3 reactor were exposed to high contamination on Thursday, officials said.
Two were taken to hospital with possible radiation burns after radioactive water seeped over their boots.
"The contaminated water had 10,000 times the amount of radiation as would be found in water circulating from a normally operating reactor," said Japanese nuclear agency official Hidehiko Nishiyama.
"It is possible that there is damage to the reactor."
Officials have previously said that small explosions at the reactor could have damaged it, but the high seepage of radiation could imply worse damage than previously believed.
The No. 3 reactor is also the only one to use plutonium in its fuel mix, which is more toxic than the uranium used in the other reactors.
Also on Friday, Japan prodded tens of thousands of more people living near Fukushima to leave, while China said two Japanese travelers arriving in the country were found to have exceedingly high radiation levels.
No one in Japan, other than the three workers at the reactor have been reported exposed to high radiation.
"Tests showed that the two travelers seriously exceeded the limit," China's General Administration of Quality Supervision, Inspection and Quarantine said, referring to radiation levels.
The agency's statement said the two travellers, who arrived in the eastern city of Wuxi from Tokyo were given medical treatment and presented no radiation risk to others.
Japan's chief cabinet secretary said 120,000 people living near Fukushima should consider leaving, although he insisted it was because getting supplies to the region was difficult and maintained it was not an evacuation order.
"Given how prolonged the situation has become, we think it would be desirable for people to voluntarily evacuate in order to meet their social needs," Yuki Edano said.
Japan evacuated a 20-km (12-mile) zone around the Fukushima nuclear plant after it was severely damaged by a killer earthquake and tsunami two weeks ago that also left more than 27,000 people dead or missing.
Seventy thousand people left their homes.
Edano has maintained there was no need currently to expand the evacuation zone, but an official at the Science Ministry confirmed that daily radiation levels in an area 30 km (18 miles) northwest of the plant exceeded the annual limit.
Safety fears at the plant and beyond -- radiation particles have been found as far away as Iceland -- are compounding Japan's worst crisis since World War Two.
As well as causing the most serious nuclear accident since Chernobyl in 1986, the magnitude 9.0 quake and ensuing wall of water that tore in from the Pacific killed 9,811 people and left 17,541 more missing, according to latest police figures.
Kyodo news agency said the death toll had topped 10,000.
Despite the increased radiation reports, there has been some progress in containing the crisis at Fukushima.
Two of the reactors are now regarded as safe in what is called a cold shutdown. Four remain volatile, emitting steam and smoke periodically, but work is advancing to restart water pumps needed to cool fuel rods inside those reactors.
"It's much more hopeful," said Tony Roulstone, a nuclear energy expert at Cambridge University.
The United States has been offering aid to its ally Japan, and two of its barges will together provide 525,000 gallons (2.0 million liters) of water for cooling the reactors.
But heightened by widespread public ignorance of the technicalities of radiation, alarm has been spreading.
Vegetable and milk shipments from the areas near the plant have been stopped, and Tokyo's 13 million residents were told this week not to give tap water to babies after contamination from rain put radiation at twice the safety level.
It dropped back to safe levels the next day, and the city governor cheerily drank water in front of cameras at a water purifying plant.
Despite government reassurances and appeals for people not to panic, there has been a rush on bottled water and shelves in many Tokyo shops remained empty of the product on Friday.
In the latest contamination finds, Kyodo reported that radioactive caesium 1.8 times higher than the standard level was found in a leafy vegetable grown at a Tokyo research facility.
Experts say radiation leaking from the plant is still mainly below levels of exposure from flights or dental and medical x-rays.
Nevertheless, Singapore, Australia, the United States and Hong Kong are all restricting food and milk imports from the zone. Other nations are screening Japanese food, and German shipping companies are simply avoiding the nation.
In Japan's north, more than a quarter of a million people are in shelters. Exhausted rescuers are still sifting through the wreckage of towns and villages, retrieving bodies and pulling out photos for the consolation of survivors.
Authorities are burying unidentified bodies in mass graves, despite Japan's usual Buddhist practice of cremation.
Amid the suffering, though, there was a sense that Japan was turning the corner in its humanitarian crisis. Aid flowed to refugees, and phone, electricity, postal and bank services began returning to the north, albeit sometimes by makeshift means.
"Things are getting much better," said 57-year-old Tsutomu Hirayama, with his family at an evacuation center in Ofunato.
"For the first two or three days, we had only one rice ball and water for each meal. I thought, how long is this going to go on? Now we get lots of food, it's almost like luxury."
The estimated $300 billion damage from the quake and tsunami makes this the world's costliest natural disaster, dwarfing Japan's 1995 Kobe quake and Hurricane Katrina in New Orleans in 2005.
Global financial market jitters over Japan's crisis have calmed, though supply disruptions are affecting the automobile and technology sectors.
Finance Minister Yoshihiko Noda said the Group of Seven rich nations would continue to monitor the foreign exchange market and cooperate again if needed after last week's intervention to curb a surge in Japan's yen currency.
Foreigner investor buying of Japanese shares actually reached a record high in the week after the disaster, data showed, as bargain-hunters leaped in when stocks first plunged.
(Additional reporting by Linda Sieg, Chizu Nomiyama, Sumio Ito, Mayumi Negishi, Shinichi Saoshiro and Kiyoshi Takenaka in Tokyo, Yoko Nishikawa, Jon Herskovitz and Chisa Fujioka in northeast Japan; Writing by Andrew Cawthorne and Raju Gopalakrishnan; Editing by John Chalmers)