Experts from the International Atomic Energy Agency have arrived in Fukushima city to observe efforts to decontaminate the area following the disaster at the Fukushima Daiichi nuclear power plant.

The 12-member team arrived as Japan announced the launch of long-term checks for thyroid abnormalities in local children.

The screenings will target 360,000 children who were aged up to 18 on 11 March, when a tsunami overwhelmed the plant, knocking out power to cooling systems and triggering meltdowns in three of its six reactors.

The IAEA inspectors will visit the facility, operated by Tokyo Electric Power (Tepco), as well as farms and schools where decontamination efforts are under way.

After the agency's first visit to the stricken plant in June, it criticised Tepco for failing to prepare for a large tsunami, but praised its post-disaster response.

The inspectors will give a preliminary report to the Japanese government at the end of next week and present more detailed findings next month.

The plant released large quantities of radioactive material over a wide area, including locations well outside the 20km (12-mile) evacuation zone imposed in the early days of the crisis.

About 100,000 people in and around the evacuation zone were forced to leave their homes; some have no idea when, or if, they will be able to return.

Health experts are particularly concerned about the possible health effects on children of long-term exposure to low levels of radiation in affected areas such as Minamisoma and Fukushima city, which has a population of almost 300,000.

The government recently lifted an advisory warning for people living in five locations between 20 and 30km from the plant to evacuate should the situation at the plant worsen, but thousands still refuse to return.

Health authorities refused to release the results of the first tests, conducted on 100 children at Fukushima Medical University.

The children will continue to be tested every two years until they reach 20, and every five years thereafter. Those found to have suffered damage to their thyroids will undergo more detailed examinations.

Children and adolescents are more at risk because their thyroids absorb radioactive iodine and other harmful substances more easily than those of adults.

Sunday's examinees included a seven-year-old boy whose parents took him out of Fukushima after the accident.

"My son hasn't shown any symptoms, but I'm worried about what might happen in four or five years from now," his mother, Kikue Komatsu, told Kyodo News. "I'm with Fukushima in spirit, but there is no way we can return while radiation levels are still high."

Last week, a Japanese charity and hospital reported that they had found thyroid irregularities in 10 out of 130 children evacuated from Fukushima prefecture.

Representatives from the Japan Chernobyl Foundation and Shinshu University hospital said they could not make a direct link between the accident and the findings, but called for children to undergo lifelong medical observations.

Health authorities in the former Soviet Union identified about 6,000 cases of thyroid cancer among people who were adolescents or children at the time of the Chernobyl disaster in 1986.

Towns outside the evacuation zone have sprayed streets with water and removed topsoil from school playgrounds in an attempt to make their communities safe.

But cleaning up the towns and villages closest to Fukushima Daiichi could take decades, the government admitted recently. Older residents in those communities accept they may be dead by the time their old homes are safe to live in .

Decontaminating areas outside the exclusion zone could take until March 2014, the Asahi Shimbun newspaper said, citing government officials.