MADRID (AP) — Activists of all ages and from all corners of the planet demanded concrete action Friday against climate change from leaders and negotiators at a global summit in Madrid.

The march was led by dozens of representatives of Latin America’s indigenous peoples — a mark of deference after anti-government protests in Chile, the original host of the summit, resulted in the the talks suddenly being moved to Europe for the third year in a row.

Celebrity climate activist Greta Thunberg declared from a stage that “change is not going to come from the people in power, it’s going to come from the masses.” A crowd of thousands responded chanting “Greta! Greta!”

Organizers claimed 500,000 people turned out for the march, but authorities in Madrid put the number at 15,000 without an immediate explanation for the disparity in the count.

The Swedish teen was followed on her first day in Madrid by a swarm of cameras and reporters, as well as curious members of the public wanting to film her on their smartphones, from the very first step she took out of an overnight train from Lisbon.

Two young activists earned cheers as they abseiled from a bridge and strung out a banner saying: “Just 8 years till 1.5 degrees C. HOW DARE YOU?” — a reference to scientists’ forecasts of rising temperatures and what activists complain is a lack of a convincing political response to the threat.

The crush as people tried to get a glimpse of Thunberg led her to pull out shortly after the start of the march, saying police had advised her to leave for safety’s sake, and she climbed into an electric car.

A Madrid police spokeswoman who spoke on condition of anonymity because she wasn’t authorized to be named in media reports said that it had only been “suggested” to that Thunberg leave after she appeared “overwhelmed” by the attention and that police never ordered the activist to abandon on safety grounds.

Earlier in the day, the 16-year-old had said at a press conference that calls for real action against climate change are still being “ignored” by political leaders despite their continuous praise of the global environmental youth movement she helped create.

Thunberg hoped the COP25 summit would lead to “something concrete” and “increasing awareness among people in general,” but she said that after more than one year of student strikes”still basically nothing has happened.”

“The climate crisis is still being ignored by those in power,” she added.

During the Dec. 2-13 talks, nearly 200 countries are meant to streamline the rules on global carbon markets and agree on how poor countries should be compensated for destruction largely caused by emissions from rich nations.