Children around the world launched another wave of school strikes demanding action on climate change Friday, in their first major action since the issue topped world leaders' agenda at the United Nations this week.

The Fridays for Future movement that began as a lone demonstration by Swedish teen Greta Thunberg just over a year ago has mushroomed, with millions of students taking to the streets of cities like New York and attracting attention in developing nations across Africa.

Some of the first protests began in New Zealand, where Thunberg said organizers estimated 170,000 people marched across the country. There were also marches in cities in Italy, Finland, Nigeria, Austria and India, among other countries.

Friday's protest followed a week of climate talks at the U.N. in New York, which included a scathing speech by Thunberg to world leaders reprimanding them for inaction.

"You have stolen my dreams and my childhood with your empty words," she said Tuesday. "The eyes of all future generations are upon you and if you choose to fail us, I say we will never forgive you."

Citing a U.N.-backed report released last year, demonstrators are demanding governments implement measures to prevent global temperatures from rising more than 2.7 degrees Fahrenheit, which scientists warn could result in dire consequences for human life and the planet.

Thunberg and the young people she has inspired say they will not stop their weekly classroom walkouts until they see a reduction in greenhouse gas emissions responsible for climate change.

In Nigeria's capital Abuja, Oladosu Adenike marked her 46th consecutive strike Friday. The activist posted images on Twitter of students dressed in blue school uniforms carrying banners with messages, "Climate change is real" and "We don't have time."

Students demonstrate during a worldwide protest demanding action on climate change, in Turin, northern Italy, on Friday. Alessandro Di Marco / AP

In Lausanne, Switzerland, where hundreds of climate strike organizers gathered in August planning for this week's events, thousands of people marched through the city, according to local reports.

Thousands more were expected to take to the streets of Helsinki, where local media reported that the city's schools would allow students to participate.

Thunberg, who remains in North America following her visit to the U.N., was scheduled to participate in climate strikes in Montreal.