Masses of children skipped school Friday to join a global strike against climate change that teens around the world hope will mark a turning point in persuading leaders to act against environmental disaster.

Some four million people filled city streets around the world, organizers said, in what was expected to be the biggest ever protest against the threat posed to the planet by rising temperatures.

Youngsters and adults chanted slogans and waved placards in demonstrations that started in Asia and the Pacific, spread across Africa, Europe and Latin America, before culminating in the United States.

Although there was no official turnout, organizers 350.org wrote on Twitter that four million people participated worldwide. The group says Friday's rallies were the start of 5,800 protests across 163 countries over the next week.

"If we actually try to make a difference we can. It's not too late yet," said 12-year-old Annabelle Abramowitz in New York, where 1.1 million students were permitted to skip school for the event.

From Berlin to Boston, Kampala to London, Seoul to Sao Paulo, protesters brandished signs with slogans including "There is no planet B" and "Make The Earth Great Again."

In Slovakia, five-year-old Teo asked a crowd of 500 "not to cut down forests, and reduce garbage production, and not to use so many petrol-fueled cars."

German Chancellor Angela Merkel used Friday to pledge at least 100 billion euros by 2030 to tackle emissions in the energy and industrial sectors, boost zero tailpipe emission electric vehicles, and get passengers out of planes and onto trains.

Events began in the deluge-threatened Pacific Islands of Vanuatu, the Solomons and Kiribati, where children chanted: "We are not sinking, we are fighting."

The defiance message was heard across the globe as children closed their textbooks in a collective call to action.

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.