Out-of-school kids and adult predators spending more time at home and on the internet during the coronavirus pandemic is the “perfect storm” driving a spike in online child sex abuse around the world, activists and police say.

From slums in the Philippines to Australia's suburbs, the cross-border crime has mushroomed as offenders take advantage of school closures and lockdowns to reach children — either in person or via social media, gaming sites and the dark web.

In Australia, federal police received more than 21,000 reports of child sex abuse in the 12 months to June 30, an increase of over 7,000 cases on the previous year, AFP reports.

Their investigators also recorded a 136 per cent increase in online child sex exploitation material.