RNZ joins more than 250 media organisations from around the world in the Covering Climate Now (CCN) initiative by committing to heighten climate coverage in the week leading up to the UN Climate Action Summit on 23 September 2019.

Millions of people around the world held a global climate strike over the last 24 hours, inspired by Swedish activist Greta Thunberg.

Students worldwide took to the streets to demand more action against climate change after an estimated 300,000 Australians gathered at rallies around the country.

From the Solomon Islands to New York's Wall Street, millions of students and workers abandoned schools and offices to demand urgent action to stop global warming.

Demonstrations that started in the Pacific islands followed the rising sun across Australia, Japan, Southeast Asia and then on to Europe, Africa, the Middle East and the Americas.

Crowds gathered in Europe, the Middle East and Africa, including London, Paris, Brussels, Berlin, Warsaw, Stockholm, Helsinki, Beirut, Nairobi and Cape Town.

Thousands of school students around New Zealand are expected to take to the streets on 27 September for the third wave of climate strike action after earlier events on 15 March and 29 May.

Ms Thunberg, who soared into prominence after sailing across the Atlantic in an emissions-free yacht ahead of the summit, was in New York to headline a massive rally in Lower Manhattan ahead of next week's climate summit at the headquarters of the United Nations.

The teenage activist was greeted like a rockstar at the rally on Friday, with chants of "Greta! Greta!" resounding around New York's Battery Park.

"This is the biggest climate strike ever in history, and we all should be so proud of ourselves because we have done this together," the teenager told demonstrators.

Ms Thunberg said about four million people took part in the strike around the world, "and we're still counting."

"This is an emergency. Our house is on fire. And it's not just the young people's house, we all live here - it affects all of us," she told the crowd.

"She's like the icon of our generation," New York protester Fiamma Cochrane, 17, said of Ms Thunberg.

Demonstrators in Paris raised a painting of Ms Thunberg in image of the Virgin Mary, a halo around her head reading, "Our house is on fire."

Alarmed by images of the Greenland ice sheets melting and the Amazon rain forests burning, the protests highlighted the leadership role of young people in the international cry to reduce consumption of fossil fuels.

Worldwide concern has escalated since United States President Donald Trump abandoned the international Paris Accord on climate change and took a series of steps to dismantle environmental protections including moving on Thursday to block stricter vehicle emissions standards in California.

"Save our planet!" marchers roared while parading from an area near Wall Street to a harbourside park with a view of the Statue of Liberty. Ms Thunberg, who tweeted pictures from the march, was scheduled to address the gathering.

Three million people had participated worldwide as of midday in New York, organisers with the anti-fossil fuels group 350 said. Britain's opposition leader Jeremy Corbyn tweeted that 100,000 people joined the demonstration in London.

"This is about my future, not only my future, but the future of my entire generation and all the generations to come after ours," said Tristan Vancleef, 16, among some 15,000 demonstrators who marched through central Brussels.

More than 200 young people in Thailand stormed into the environment ministry and dropped to the ground feigning death as they demanded government action, while students in New Delhi staged a similar "die-in."

Activists in Berlin and Munich re-enacted gallows, standing on melting blocks of ice with nooses around their necks to symbolise the death that awaits them when the polar ice caps melt. Others in Warsaw staged a performance of people drowning in a sea of plastic waste.

While Europeans filled the streets, students in the Solomon Islands gathered at the rising ocean water's edge wearing traditional grass skirts. The issue is vital to low-lying Pacific islands, which have repeatedly asked wealthier nations to do more to prevent rising sea levels.

"There is no Planet B," read a sign hoisted by a young woman in London.

In Kenya, around 500 activists marched through the streets demanding that the government cancel plans for a controversial coal plant and investigate corruption in hydropower dams.

"In Samburu there is a lot of heat, the grass has dried up, there is little water," said Francis Lentel, a young herdsman in traditional beads, holding a picture of the Earth weeping.

Social media posts showed demonstrations ranging from a few dozen primary school children in Abuja, Nigeria, to tens of thousands of people in cities from Hamburg, Germany to Melbourne, Australia.

"Make love, not CO2" signs were spotted in Berlin and Vienna.

"Our oceans are rising, so are we," was a popular slogan on placards in many places.

Global warming caused by heat-trapping greenhouse gases from burning fossil fuels has already led to droughts and heat waves, melting glaciers, rising sea levels and floods, according to scientists.

Carbon emissions climbed to a record high last year, despite a warning from the United Nations-backed Intergovernmental Panel on Climate Change in October that output of the gases must be slashed over the next 12 years to stabilise the climate.

The protest movement is putting increasing pressure on both governments and companies to respond.

German Chancellor Angela Merkel unveiled a major new climate protection package thrashed out by parties in her coalition in all-night talks.

The UN summit next week brings together world leaders to discuss climate change mitigation strategies, such as transitioning to renewable energy sources.

Mr Trump and Brazilian President Jair Bolsonaro, among the world's only national leaders who publicly question climate science, are not due to take part, their representatives said.

Danielle Porepilliasana, a Sydney high school student, had a blunt message for politicians such as Australian Finance Minister Mathias Cormann, who told parliament on Thursday that students should stay in class.

"World leaders from everywhere are telling us that students need to be at school doing work," she said, wearing anti-coal earrings. "I'd like to see them at their parliaments doing their jobs for once."