Swedish activist Greta Thunberg has told a crowd of 200 climate change protestors to “never give up” the fight as they gathered outside the White House in Washington.

The weekly protest by the Washington chapter of the Fridays for Future movement was suddenly in sharp focus as Thunberg, who has become an icon of the struggle against the climate crisis, set about addressing the mostly-teenage crowd on Friday local time.

US President Donald Trump, who has described climate change as a “hoax” perpetrated by China to hamper the US economy, withdrew the United States from the 2015 Paris Agreement, which set targets for the reduction of emissions of greenhouse gases.

Thunberg says the movement will not relent in its demands for action.

“I just want to say I’m so incredibly grateful for every single one of you, I’m so proud of you, who have come here, and I – it’s a lot of people.

“This is overwhelming,” she told a crowd gathered across the street from the White House.

“Just never give up, we will continue and see you next week,” Thunberg said, referring to the Global Climate Strike planned for September 20.

16-year-old climate activist Greta Thunberg and other young protesters rallied outside the White House, calling for urgent action on the climate crisis https://t.co/FyWXMDGrjT pic.twitter.com/bolUPZMthy

— CNN (@CNN) September 14, 2019

In August 2018, Thunberg, then 15, began skipping school on Fridays to demonstrate outside Sweden’s parliament.

Her example has been emulated by thousands of students worldwide, giving rise to the movement.

Yet, much as she did two weeks ago outside UN headquarters in New York, the young Swede preferred to leave the speechmaking to other activists, spending most of the time in the background.

Hundreds of young protestors gathered across the street from the White House on Friday local time. Photo: AAP

Among those who did speak was Jonah Gottlieb, 17, the executive director of the National Children’s Campaign, who said that the aim of the protests was to “send a message” to the people in power.

“They know that we’re coming after them,” he said.

“This is our planet and we are here to stay!”

The crowd also heard from Nadia Nazar, the 16-year-old founder of the group Zero Hour.

“We’re striking today to save tomorrow, not to save life in 50 years but to save tomorrow,” she said.

Ella Jacobs, also 16, said Mr Trump needed to “listen to the science” regarding climate.

Greta Thunberg arrives in the US. Photo: Getty

Thunberg, who refuses to fly and instead arrived on US soil via a multi-million dollar racing yacht, will address the September 23 United Nations Climate Action Summit in nine days.

The yacht Malizia II, which is skippered by Pierre Casiraghi – son of Monaco’s Princess Caroline – and German distance sailor Boris Herrmann, offered Thunberg a ride to New York.

The carbon-free vessel, which relies on solar panels and hydro-turbines for auxiliary power and is equipped with sensors that collect data on ocean acidity, sailed from Plymouth, in southern England, on August 14, and reached New York two weeks later.

-with AAP