We will continue to school-strike until they do something, says Greta Thunberg

Swedish climate activist Greta Thunberg who has sparked school strikes worldwide against global warming joined thousands of students in Hamburg on Friday, urging them to stay angry and fight for change.

"Yes, we are angry. We are angry because the older generations are continuing to steal our future right now," the 16-year-old activist told a cheering crowd from a stage in Hamburg.

"For way too long the politicians and the people in power have gotten away with not doing anything to fight the climate crisis," she said.

"But we will make sure that they will not get away with it any longer. We will continue to school-strike until they do something."

Her short speech drew loud applause in the northern port city, where police say some 4,000 demonstrators hit the streets, carrying signs that read "No more excuses, it's time to save our world" and "The climate is changing, why aren't we?".

Other placards paid tribute to the Swedish teenager with slogans like "Make the world Greta again" and "Team Greta", adorned with a drawing of her trademark braids.

With the "Fridays for Future" school strikes, Thunberg has inspired a global movement that began with her solitary protest outside the Swedish Parliament in Stockholm last August.

Since then, tens of thousands of pupils in cities across Europe and as far away as Australia, Uganda, Mexico and the United States have walked out of their Friday classes to push for more ambitious carbon-cutting targets.

Now the face of her generation's climate activism, Thunberg has used her current school holidays to join protests elsewhere, marching in Paris, Brussels and Antwerp.

She has also taken her message to world leaders directly in recent months, including at an EU conference last week where she urged the bloc to double its ambitions for greenhouse gas cuts.

Under the 2015 Paris deal to cap the rise in global warming to well below 2 degrees Celsius, the European Union has pledged to cut emissions by at least 40 percent by 2030, compared to 1990.

The "Fridays for Future" movement is planning a coordinated, global strike on March 15 that promises to be the biggest mobilisation in the campaign to date.

The school strikes have since December gained particularly strong momentum in Germany -- a country that despite its green reputation is a major emitter of greenhouse gases, in part because of its ongoing reliance on coal, the dirtiest fossil fuel.

A government-appointed committee recently urged Germany to shut down its coal-fired power plants by 2038 but critics say that isn't fast enough.