* Neighbours take fright over radiation threat
* Expert says levels not dangerous
* Tourist arrivals plunge in peak season
* Sparks debate over nuclear safety in the U.S. (Adds TEPCO statement, trace radioactivity detected in China)
By Kiyoshi Takenaka and Yoko Nishikawa
TOKYO, April 7 (Reuters) - Japan's neighbours sounded increasingly alarmed over the risk of radiation from the crippled Fukushima nuclear power plant, while figures showed the number of foreign visitors to the country had slumped during what should be the peak tourist season.
The world's worst nuclear disaster in 25 years is also raising concern over safety in the United States, which has more atomic reactors than any other country, especially at one plant which is similar to the one in Fukushima wrecked by last month's 9.0 magnitude earthquake and tsunami.
Engineers, who sealed a leak this week that had allowed highly radioactive water into the sea, are now pumping nitrogen into one reactor to prevent the risk of a hydrogen gas explosion, and want to start the process in another two reactors.
Operator Tokyo Electric Power Co (TEPCO) said late on Thursday it did not expect it would have to dump any more contaminated water into the ocean after Saturday.
Earlier, TEPCO said the chance of a repeat of the gas explosions that damaged two reactors in the first days of the disaster was "extremely small".
But as engineers battle multiple crises -- some the result of efforts to try to cool reactors -- officials admit it could take months to bring the reactors under control and years to clear up the toxic mess left behind at the plant 240 km (150 miles) north of Tokyo.
"Data shows the reactors are in a stable condition, but we are not out of the woods yet," Chief Cabinet Secretary Yukio Edano told reporters.
The government has already set up a 20 km (12 miles) exclusion zone around the plant, banned fishing along much of the northeast coast and set up evacuation centres for the tens of thousands forced to leave their homes following the crisis.
The March 11 quake and giant tsunami waves it triggered killed, or left missing, about 28,000 people.
Trace levels of radioactive material have been detected in the air in 22 Chinese provinces but the amounts did not pose a threat to health or the environment, China's state news agency Xinhua said.
Earlier, China's Health Ministry said traces of radioactivity in spinach had been found in three provinces. [ID:nL3E7F62LF]
India has banned Japanese food imports for three months. [ID:nL3E7F606G]
In South Korea, some schools closed because parents were worried that rain across the country could be toxic.
"We've sent out an official communication today that schools should try to refrain from outdoor activities," an education official in South Korea said. [ID:nL3E7F7077]
South Korea's nuclear safety agency reported a small level of radioactive iodine and caesium particles in rain but said it was not enough to be a public health concern.
The few schools that closed on Thursday were expected to reopen on Friday if the rain stopped.
CRITICISM
There has been repeated criticism of Japan for a lack of information about the crisis.
In Vienna on Wednesday, Japanese nuclear officials faced some tough questioning from other countries, diplomatic sources said. "People were asking pointed questions seeking information, the Russians were critical," one source said after the closed-door meeting, part of a conference scheduled long before earthquake.
The source said a Russian official at the meeting had suggested there was a need for an improved emergency reaction.
Though Japan's capital is back to normal almost four weeks after the disaster, foreign tourists are staying away. Many airlines have reduced flights to Japan .
This week is the peak of the cherry blossom season which normally attracts large numbers of tourists. But government figures released showed that compared with the same time a year ago, the number of visitors since March 11 had tumbled 75 percent.
Japan's central bank highlighted the risks for an already fragile economy at the end of its two-day policy review.
"Japan's economy is under strong downward pressure, mainly on production, due to the earthquake," the Bank of Japan said after the review at which it kept interest rates unchanged and launched measures to help banks in the devastated northeast.
It also cut its economic assessment and warned of more uncertainty over the outlook, signalling it stood ready to ease monetary policy further as the nuclear crisis and rolling power blackouts hit output and business sentiment. [ID:nL3E7F70JG]
The government is discussing an emergency budget, expected to be about 4 trillion yen ($47 billion), to help with recovery and reconstruction but there is no agreement on how to raise money in a country where public debt is already nearly double the size of the economy.
SAFETY CONCERNS
In Vienna, the head of a U.N. scientific body said the accident at the Fukushima Daiichi plant was not expected to have any serious impact on health, based on information he had.
Wolfgang Weiss, chairman of the United Nations Scientific Committee on the Effects of Atomic Radiation, said the disaster was less dramatic than Chernobyl in 1986 but "much more serious" than Three Mile Island in the United States in 1979.
"We have seen traces of iodine in the air all over the world now but they are much, much, much lower than traces we have seen at similar distances after Chernobyl," he added. [ID:nLDE73529F]
In Washington, Democratic lawmakers raised concern about whether regulators and the nuclear power industry were doing enough to ensure U.S. reactors could withstand worst-case scenarios.
Worries focused on a Pennsylvania nuclear plant with the same kind of reactor design as the Fukushima plant.
Some lawmakers argued that the U.S. plant could be at risk of meltdown in the case of a severe emergency. [ID:nL3E7F62A5]
The U.S. Nuclear Regulatory Commission is conducting special inspections at two Illinois nuclear plants operated by Exelon Corp after routine checks in February found a problem with backup pumps that would be used to remove heat from the reactors in case of an accident. ($1=85.475 Japanese yen) (Additional reporting by Mayumi Negishi in Tokyo, Sui-lee Wee in Beijing, Roberta Rampton and Ayesha Rascoe in Washington, Scott DiSavino in New York, Jack Kim in Seoul and Fredrick Dahl in Vienna; Writing by Jonathan Thatcher and Daniel Magnowski)