Thirteen percent of elementary to high school students in Japan had depressive tendencies warranting medical attention last October due to the effects of the coronavirus pandemic, a recent study by a medical institute said.

Behavioral restrictions to prevent the spread of the virus, such as wearing masks and eating meals without conversing, are believed to have been among the factors affecting children's mental well-being, the National Center for Child Health and Development said.

The survey was conducted on around 3,000 students in fifth grade through the first year of high school, with some 60% or around 1,900 of them responding, the Tokyo-based institute said in the study published in late April.

Depressive tendencies were determined by monitoring symptoms, including the frequency of depression, inability to concentrate and acts of self-harm.

The survey found that 13% of the respondents had moderate to more severe symptoms that would have warranted a visit to a hospital.

The figure was larger than the 6% seen in 2020 and 11% in 2021, although the grades covered were different in the previous surveys, it said.

Even though COVID-19 restrictions have since been eased, the institute warned that some children would need time to recover mentally and physically.

"Adults need to be attentive to children even more than usual and listen to them," said Naho Morisaki, the head of the center's Department of Social Medicine.

The center plans to continue its study on the pandemic's effect on children's health, it said.