UN Secretary-General Antonio Guterres said Tuesday the coronavirus pandemic has led to the largest disruption of education in history, with schools closed in more than 160 countries in mid-July, affecting over 1 billion students.

In addition, the UN chief said at least 40 million children worldwide have missed out on education "in their critical preschool year."

As a result, Guterres warned that the world faces "a generational catastrophe that could waste untold human potential, undermine decades of progress, and exacerbate entrenched inequalities."

Even before the pandemic, Guterres said, the world faced "a learning crisis," with more than 250 million children out of school, and only a quarter of secondary school youngsters in developing countries leaving school "with basic skills."

According to a global projection covering 180 countries by the UN education agency UNESCO and partner organizations, some 23.8 million additional children and youths from pre-primary school to university level are at risk of dropping out or not having access to school next year due to the pandemic’s economic impact.

"We are at a defining moment for the world’s children and young people," Guterres said in a video message and a 26-page policy briefing. "The decisions that governments and partners take now will have lasting impact on hundreds of millions of young people, and on the development prospects of countries for decades to come."

According to the policy briefing, "the unparalleled education disruption" from the pandemic is far from over and as many as 100 countries have not yet announced a date for schools to reopen.

Guterres called for action in four key areas, the first being reopening schools.

"Once local transmission of COVID-19 is under control," he said, "getting students back into schools and learning institutions as safely as possible must be a top priority."

UNESCO’s Assistant Director-General for Education Stefania Giannini told reporters the Paris-based agency plans to hold a high-level virtual meeting in the fall, likely during the second half of October, to secure commitments from world leaders and the international community to place education at the forefront of recovery agendas from the pandemic.

"There may be economic trade-offs, but the longer schools remain closed the more devastating the impact, especially on the poorest and most vulnerable children," Giannini warned.

She stressed that schools are not only for learning but provide social protection and nutrition, especially for vulnerable youngsters.

The coronavirus crisis has amplified digital, social and gender inequalities, Giannini said, with girls, refugees, the disabled, displaced and youngsters in rural areas the most vulnerable and facing limited opportunities to continue their learning.

Guterres said increasing financing for education must be given priority.

Before the pandemic, low- and middle-income countries faced an education funding gap of $1.5 trillion annually, he said, and the gap in education financing globally could increase by 30 percent because of the pandemic.

The secretary-general said education initiatives must target "those at greatest risk of being left behind," including youngsters in crises, minorities, and the displaced and disabled. And these initiatives should urgently seek to bridge the digital divide that has become even more evident during the COVID-19 crisis, he said.

On a positive note, Guterres said the pandemic is providing "a generational opportunity to reimagine education" and leap forward to systems that deliver quality education.

To achieve this, he called for investments in "digital literacy and infrastructure" and education systems that are more flexible, equitable and inclusive.

UNESCO’s Giannini said innovations made so far during the pandemic, including online learning and education on radio and television, "proves change can happen quickly."

She said a coalition of global organizations launched a campaign Tuesday called "Save Our Future" to amplify the voices of children and young people and urge governments worldwide to recognize that investing in education is critical to COVID-19 recovery and to the future of the world.