Schools remain shut in 19 countries due to the pandemic, affecting 156 million children in what risks being "a generational catastrophe," the heads of two UN agencies warned Monday.

The statement from the leaders of UNICEF and UNESCO, responsible for children's issues and education, said "governments have too often shut down schools and kept them closed for prolonged periods, even when the epidemiological situation didn't warrant it." 

They advised that "schools should be the last to close and the first to reopen," with the effects of closures ranging from lower educational achievement to mental health problems and increased malnutrition.

"We urge decision-makers and governments to prioritise the safe reopening of schools to avoid a generational catastrophe," UNICEF leader Henrietta Fore and UNESCO chief Audrey Azoulay wrote.

"Closing schools mortgages our future for unclear benefits to our present. We must prioritise better. We can re-open schools safely, and we must," they added.