Some 10,000 children whose families fled Fukushima Prefecture due to the March 2011 nuclear disaster have yet to return, prefectural government officials said Thursday.

Five years after the earthquake and ensuing tsunami triggered the radiation crisis at the Fukushima No. 1 nuclear complex, families with children continue to have serious reservations about environmental safety, according to a recent survey by the prefectural government.

As of last October, the number of such minors who have evacuated to areas outside the prefecture stood at 10,557. Among them, 4,760 were from 12 coastal municipalities designated as evacuation zones in the nuclear crisis, the survey said. The prefecture has 59 municipalities.

With young people absent from those areas, reconstruction may be difficult in the future, experts say.

"We need to implement more measures to improve the child-rearing environment (for their parents) to enable those children to return home" because the children are with their families, a prefectural government official from its children and youth division said.

The prefectural government has since October 2012 allocated subsidies to make medical costs free for children under 18. Last year, it began subsidizing moving expenses for evacuees wanting to return to their hometowns.

Officials say despite the recent tally, the actual number of children evacuees may be higher, with some families believed to have transferred their resident registration to the municipalities where they fled.

There were about 18,000 child evacuees as of April 2012. The number gradually declined after evacuation orders for some municipalities were lifted when radiation doses dropped following decontamination works. As of Feb. 1, the prefecture's population stood at around 1.91 million.