The COVID-19 pandemic has created the largest disruption to education in history and prolonged school closures could further entrench inequalities in access to learning, United Nations Secretary-General Antonio Guterres said on Tuesday, underlining the need for "bold steps" to address the crisis.

Describing education as "the key to personal development and the future of societies," he issued recommendations to get children back in the classroom in a policy brief launched alongside a new global campaign called "Save our Future."

"As the world faces unsustainable levels of inequality, we need education, the great equalizer, more than ever," he said in a video message, adding that "we must take bold steps now, to create inclusive, resilient, quality education systems fit for the future."

The United Nations estimates that the pandemic has affected at least one billion students worldwide.

Despite efforts to continue learning during the crisis, including through delivering lessons by radio, television and online, many are still not being reached.

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.

The policy brief calls for action in four key areas, starting with the re-opening of schools once local transmission of COVID-19 is under control.

The UN chief also called for greater investment in education, as low- and middle-income countries had already faced an annual funding gap of 1.5 trillion U.S. dollars prior to the pandemic.

As of early Tuesday, there were 18,288,573 confirmed COVID-19 cases around the world, and 693,968 dead globally due to the novel coronavirus pandemic, according to the latest data from Johns Hopkins University.

(With input from agencies)