Demonstrators of all ages braved chilly spring temperatures of 3C (37F), wearing parkas and woolly bonnets and chanting "International solidarity! We only have one planet!" and "(Climate Minister Romina) Pourmokhtari's empty words won't save our planet", according to an AFP journalist at the scene.

The march was organised by the Fridays For Future (FFF) movement.

"We're gathered here to fight, once again, for climate justice," Thunberg told AFP.

"It's now been more than five and a half years that we've been doing the same thing, organising big global strikes for the climate and gathering people, youths from the entire world."

The first global youth climate strike, started by Thunberg and the Fridays for Future movement, attracted thousands of people on March 15, 2019.

Six months later, in September 2019, the movement had mushroomed, with millions of people marching around the planet for the climate.

The Swedish activist became an international name in August 2018 when she began her "School Strike for the Climate" at the age of 15, sitting outside Sweden's parliament every Friday morning.

She still takes part regularly in marches and other events where she criticises the lack of political action to halt global warming.

"We are many people and youths who want to express our frustration over what decision-makers are doing right now: they don't care about our future and aren't doing anything to stop the climate crisis," Karla Alfaro Gripe, an 18-year-old FFF activist, told AFP.

The Swedish Climate Policy Council, tasked with evaluating the government's policy, said last month that Sweden will not be able to meet its 2030 emissions reduction target after adopting measures in 2023 that will lead to short-term emissions increases.

Climate Minister Romina Pourmokhtari said at the time she was "not particularly worried about some of the assessments" in the council's report, noting that several of the issues raised had already been addressed with "measures" added afterwards.