Children across Asia and the Pacific kicked off what are set to be the largest global climate protests in history on Friday, demanding adults’ act now to stop environmental disaster.

From Sydney to Seoul, Manila to Mumbai, children heeded the rallying cry of fellow teen activist Greta Thunberg and shut their textbooks in a collective call to action.

In Australia, more than 300,000 kids, parents and supporters rallied, organizers said, more than double the turnout at climate strikes in March, and among the first of 5,000 events planned worldwide by a movement dubbed “Fridays for Future”.

They are demanding politicians and businesses take drastic action to stop global warming, which scientists warn will lead to environmental catastrophe on current trends.

The day of protests is already eclipsing crowd numbers seen in strikes last May and will culminate in New York, where 1.1 million students in around 1,800 public schools have been permitted to skip school.

In India, schoolchildren rallied in New Delhi and Mumbai while thousands protested in the Philippines, which experts say faces threats from rising sea levels and increasingly violent storms.