Thousands of environmental activists have staged a rally outside Germany's parliament two days before the country holds a national election to demand that politicians take stronger action to curb climate change.

The protest outside the Reichstag in Berlin was part of a string of rallies around the world amid dire warnings that the planet faces dangerous temperature rises unless greenhouse gas emissions are cut sharply in the coming years.

The idea for a global "climate strike" was inspired by teenage Swedish activist Greta Thunberg's solo protest in Stockholm three years ago.

It snowballed into a mass movement until the coronavirus pandemic put a stop to large gatherings. Activists have only recently started staging smaller gatherings.

German activists have referred to Sunday's election as the "vote of the century", arguing that the decision taken by the next government will influence the country's efforts to tackle climate change for decades.

Friday's rally was a multi-generational event, drawing school-age participants as well as adults.

Rene Bohrenfeldt, an IT expert taking part in the Berlin rally, said he hoped older Germans would consider the issue when casting their votes on Sunday.

"The majority of voters are older than 50 and determine the outcome of the election," he said. "I appeal to all grandmothers to make the right decision for the climate and for their grandchildren."

Christiane Koetter-Lietz, who attended with her children and grandchildren, said she would be voting for Germany's Green party, which has campaigned for tougher measures to cut the country's greenhouse gas emissions.

"We have water catastrophes, fire catastrophes, the world is burning. This is the very last warning," said the 69-year-old.

Global warming has also been a top election issue in Iceland, where voters heads to the polls for a general election on Saturday.

All parties running for seats in the North Atlantic island nation's parliament acknowledge global warming as a force of change in a sub-Arctic landscape but disagree on how to respond to it.

Other demonstrations were held across Europe, including in Italy and the UK, and around the world in countries such as India and Japan