Ahead of a climate strike in the streets of Madrid, Greta Thunberg and other young climate campaigners on Friday held a silent sit-in in the halls of the COP 25 United Nations conference in the Spanish capital in a display of frustration and anger over government inaction on the planetary emergency.

David Fopp, a founding member of Extinction Rebellion in Sweden, called the youth action the "most powerful and strong statement you can imagine."

Global climate movement 350.org, in a tweet, said the action was meant "to get government leaders to WAKE UP."

"We need climate action and we need change right now. And the time to act is now," said 22-year-old Hilda Flavia Nakabuye of Uganda, a self-declared "victim of this climate crisis," as she took part in the protest.

#FridaysForFuture youth strikers are keeping the pressure on world leaders at #COP25. Hilda from Uganda during the youth-led sit-in: "We need #climateaction and we need change right now." pic.twitter.com/B1xKbWvfsv — 350 dot org (@350) December 6, 2019

Press at the conference appeared to pay little attention to the sit-in until Thunberg—who'd arrived in Madrid by train earlier in the day—joined them, according to tweets posted by climate reporter Chloé Farand.

@GretaThunberg has now joined the sit-in. Here's the media madness around her and other young strikers now pic.twitter.com/uFpa73IIFV — Chloé Farand (@ChloeFarand) December 6, 2019

Climate activists at COP 25 will amplify their demand for urgent action on Wednesday with a strike in Madrid set to kick off at 6pm local time.

Tomorrow December 6th we strike again around the world for the climate!

I’ll join the strike in Madrid at #COP25 18.00 at Atocha! See you there!#FridaysForFuture #ClimateStrike #schoolstrike4climate pic.twitter.com/bD5VYXFtqV — Greta Thunberg (@GretaThunberg) December 5, 2019

Climate strikes in other cities across Europe and beyond are also set to take place Friday.