By Taiga Uranaka and Shinichi Saoshiro
TOKYO (Reuters) - Japanese engineers struggled on Sunday to pump radioactive water from a crippled nuclear power station while the United Nations' chief nuclear inspector said the crisis triggered by this month's earthquake and tsunami was far from over.
Radiation levels in the sea off the Fukushima Daiichi plant rose on Sunday to 1,850 times normal just over two weeks after the disaster struck, from 1,250 on Saturday, Japan's Nuclear and Industrial Safety Agency said.
The radiation particles will be dispersed and diluted, however, posing no threat to marine life or food safety, a senior agency official said.
"There is no need to worry about health risks," Hidehiko Nishiyama said.
The crisis at the plant, 240 km (150 miles) north of Tokyo, has overshadowed a relief and recovery effort from the magnitude 9.0 quake and the huge tsunami it triggered on March 11 that left more than 27,100 people dead or missing in northeast Japan.
Yukiya Amano, the director general of the U.N. International Atomic Energy Agency (IAEA), cautioned that Japan's nuclear emergency could go on for weeks, if not months more.
"This is a very serious accident by all standards," he told the New York Times. "And it is not yet over."
Amano, a former Japanese diplomat who visited Japan after the quake, said authorities were still unsure about whether the plant's reactor cores and spent fuel were covered with the water needed to cool them.
He told the newspaper he saw a few "positive signs" with the restoration of some electric power to the plant. But he said: "More efforts should be done to put an end to the accident," while adding he was not criticising Japan's response.
The IAEA, the U.N. nuclear watchdog, said it had sent two additional teams to Japan over the past two days, one to help in monitoring radiation and one to assess food contamination.
The Japanese government estimated last week the material damage from the March 11 catastrophe could top $300 billion, making it the world's costliest natural disaster.
In addition, power cuts have disrupted production while the drawn-out battle to prevent a meltdown at the 40-year-old plant has hurt consumer confidence and spread contamination fears well beyond Japan.
U.N. Secretary-General Ban Ki-moon said it was time to reassess the international atomic safety regime.
Japan's nuclear crisis also looks set to claim its first, and unlikely, political casualty. In far away Germany, Chancellor Angela Merkel's party faces a defeat in a key state on Sunday, largely because of her policy U-turns on nuclear power.
Engineers trying to stabilize the plant have to pump out radioactive water found in buildings housing three of the six reactors.
On Thursday, three workers were taken to hospital from reactor No. 3 after stepping in water with radiation levels 10,000 times higher than usually found in a reactor. That raised fear the core's container could be damaged.
An official from plant operator Tokyo Electric Power Co (TEPCO) told a news conference experts still had to determine where to put some of the contaminated water while engineers were still trying to fully restore the plant's power.
Two of the plant's reactors are now seen as safe but the other four are volatile, occasionally emitting steam and smoke. However, the nuclear safety agency said on Saturday that temperature and pressure in all reactors had stabilized.
The government has said the situation was nowhere near to being resolved, although it was not deteriorating.
"We are preventing the situation from worsening," Chief Cabinet Secretary Yukio Edano told a news conference on Saturday. "But there is still no room for complacency."
RADIATION LEVELS LOW
When a reactor exploded at Chernobyl in Ukraine in 1986 leading to the world's worst nuclear accident, it took weeks to "stabilize" the reactor's remains and months to clean up radioactive materials and cover the site with a concrete and steel sarcophagus.
So far, no significant levels of radiation have been detected beyond the vicinity of the plant in Fukushima.
The U.S. Department of Energy said on its website (http://blog.energy.gov/content/situation-japan/)
no significant quantities of radiological material had been deposited in the area around the plant since March 19, according to tests on Friday.
In Tokyo, a metropolis of 13 million, a Reuters reading on Sunday morning showed ambient radiation of 0.22 microsieverts per hour, about six times normal for the city. That was well within the global average of naturally occurring background radiation of 0.17-0.39 microsieverts per hour, a range given by the World Nuclear Association.
In the city of Yamagata, 110 km (70 miles) northwest of Fukushima, the reading was 0.15 microsieverts per hour.
The government has prodded tens of thousands of people living in a 20-30 km (12-18 mile) zone beyond the stricken complex to leave. Edano said the residents should move because it was difficult to get supplies to the area, and not because of elevated radiation.
Kazuo Suzuki, 56, who has moved from his house near the plant to an evacuation center, said neighbors he had talked to by telephone said delivery trucks were not going to the exclusion zone because of radiation worries.
"Goods are running out, meaning people have to drive to the next town to buy things. But there is a fuel shortage there too, so they have to wait in long queues for gasoline."
Radiation levels at the evacuation center were within a normal range of about 0.16 microsievert, according to a Reuters Geiger counter reading.
In Japan's northeast, more than a quarter of a million people remain in shelters, and the impact on livelihoods of fishing communities is becoming clearer.
Police crews on Sunday pulled two bodies out of a vast field of debris from shattered houses more than one mile from the ocean in Rikuzentakata, north of Sendai.
As the search for bodies ground on, shattered towns along the coast cremated the dead in facilities stretched beyond capacity. Bodies that could not be handled in crematoriums were buried in makeshift mass graves hastily dug by engineering crews from Japan's Self-Defense Forces.
(Additional reporting by Yoko Kubota, Chizu Nomiyama and Phil Smith in Tokyo, Paul Eckert in Rikuzentakata, Writing by Tomasz Janowski; Editing by Raju Gopalakrishnan)