Nearly half of Japan's municipalities are likely to see their populations young women shrink by more than half by 2040 compared with 2010 if the flight to major cities continues apace, a study by the Japan Policy Council said Thursday.

The demographic prediction was made by a panel of experts in the think tank who warn that local communities will likely break down and that towns and other local authorities may find it difficult to operate because of ongoing population decline prompted in part by a drop in age groups that are actively reproducing.

The panel, headed by Hiroya Masuda, former minister of internal affairs, recommends rectifying "the overconcentration" in Tokyo and building attractive cities to keep regional economies vibrant.

Based on data from the National Institute of Population and Social Security Research, the panel estimated that in 2040, 896 municipalities — or 49.8 percent of all municipalities — would see their ratios of women in their 20s and 30s sink by more than half from what they were in 2010.

With the increase in seniors living in big cities, there will be an endless stream of people moving from regional towns and cities to work in the medical and elderly care sectors, according to the panel.

In making its estimate, the Japan Policy Council panel assumed that between 60,000 and 80,000 people will flow into big cities from smaller towns and cities each year, at the current pace.

In a similar study, the National Institute of Population and Social Security Research found that 373 municipalities, or 20.7 percent, would see their populations of young women fall by more than half by 2040, assuming that the exodus from regional towns and cities gradually dwindles.