A teacher welcomes pupils back to school on the first day of school following the summer holidays. At Lankow primary school in Schwerin, Germany, on Aug 3, 2020. (JENS BUETTNER / DPA VIA AP)

UNITED NATIONS - UN Secretary-General Antonio Guterres warned on Tuesday that the world faces a "generational catastrophe" because of school closures amid the coronavirus pandemic and said that getting students safely back to the classroom must be "a top priority".

Guterres said that as of mid-July schools were closed in some 160 countries, affecting more than 1 billion students, while at least 40 million children have missed out on pre-school.

Guterres said that as of mid-July schools were closed in some 160 countries, affecting more than 1 billion students, while at least 40 million children have missed out on pre-school

This came on top of more than 250 million children already being out of school before the pandemic and only a quarter of secondary school students in developing countries leaving with basic skills, he said in a video statement.

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"Now we face a generational catastrophe that could waste untold human potential, undermine decades of progress, and exacerbate entrenched inequalities," said Guterres as he launched a UN "Save our Future" campaign. 

The UN chief said that "learners with disabilities, members of minority or disadvantaged communities, as well as refugees and displaced persons, are among those at highest risk of being left behind".

Guterres issued recommendations to resume classes in a policy brief that called for action in key areas, starting with the reopening of schools once local transmission of COVID-19 is under control.

"Once local transmission of COVID-19 is under control, getting students back into schools and learning institutions as safely as possible must be a top priority," he said. "Consultation with parents, carers, teachers and young people is fundamental."

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The UN chief called for greater investment in education as low- and middle-income countries had already faced an annual funding gap of US$1.5 trillion in schooling prior to the pandemic, saying that "education budgets need to be protected and increased".

Education initiatives must also seek to reach those at greatest risk of being left behind, he said.

Guterres highlighted what he saw as the "generational opportunity" to deliver quality education for all children, in line with the UN's Sustainable Development Goals.

"To achieve this, we need investment in digital literacy and infrastructure, an evolution towards learning how to learn, a rejuvenation of life-long learning and strengthened links between formal and non-formal education," Guterres said.

The UN recommendations for getting global education back on track come as US President Donald Trump pushes for schools to reopen in the face of opposition from some teachers and parents while COVID-19 is surging in many parts of the country.

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The coronavirus has infected 4.7 million people in the United States and killed more than 155,000 Americans since February, according to a tally by Johns Hopkins University (JHU). 

Globally, the coronavirus has infected at least 18.2 million people and there have been more than 693,000 known deaths worldwide, according to JHU's tally.