Schoolchildren attend a protest march as part of the world's largest climate strike in Sydney, Australia.

Young people across the world are taking part in the “Global Climate Strike” Friday — with students in Australia kicking off the day of demonstrations ahead of a United Nations summit in New York.

Organizers estimated more than 300,000 protesters — many of them children who skipped school — descended on streets Down Under to demand action to reduce greenhouse gas emissions.

“Even though we ourselves aren’t sick, the planet which we live on is, and we are protesting and fighting for it,” said Siobhan Sutton, a 15-year-old student at Perth Modern School.

More than 4,600 events in 139 countries are scheduled between Sept. 20 and 27, according to Swedish teenage climate activist Greta Thunberg.

Smaller protests took place Friday in Asia — from the Philippines to Hong Kong and India.

The UN will host a youth climate summit Saturday, as well as a climate action summit Monday.

All 1.1 million students in New York City schools will be excused to attend the protests Friday — a move supported by Mayor Bill de Blasio, who previously tweeted, “Today’s leaders are making decisions for our environment that our kids will have to live with. New York City stands with our young people. They’re our conscience.”

With Post wires