Tens of thousands of protesters gathered outside Germany's parliament on Friday calling on authorities to take stronger action against climate change.

It comes only two days before the country holds a national election that will designate chancellor Angela Merkel's successor after her almost 16 years in power.

Swedish activist Greta Thunberg, 18, addressed the Berlin crowd from a stage, urging voters to keep politicians under constant pressure over climate change.

"We must keep going into the streets and we must keep demanding our leaders to take real climate action. We must never give up. There's no going back now", she said.

“We can still turn this around,” she added. “We demand change, and we are the change.”

The Berlin protest was part of a string of rallies around the world, from Japan and Italy to India, Austria and Britain.

The climate issue has been a major topic during Germany's election campaign.

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 to come.

German Environment Ministry spokesman Nikolai Fichtner said pressure from climate activists already resulted in concrete policies in recent years, from higher carbon prices to billions of euros invested in greener technologies.

“We also have a new mood across society, where politicians [...] have to explain why they're not protecting the climate", he added.