Washington DC - Thousands of people descended Saturday on Washington's National Mall and rallied in other cities across the US and abroad in opposition to the policies of Donald Trump, in the largest protests since he returned to the presidency.

A big "HANDS OFF!" banner stretched across the stage of an outdoor theater just a few blocks from the White House, with protesters holding signs that read "Not My President," "Fascism has Arrived," "Hands Off Our Social Security," and "Wake Up and Smell the Coup."

Jane Ellen Saums (66) said she was dismayed to see the Trump administration dismantling America's long-standing democratic institutions.

"It's extremely concerning to see what is happening to our government, and all of the checks and balances that have been put in place that are being totally run over – everything from the environment to personal rights," said the real estate worker who came dressed as Mother Nature, wrapped in ivy and holding a globe.

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At a time of spreading global resentment against the Republican president – heightened by his announcement Wednesday of sweeping tariffs against scores of countries – demonstrators also marched in several European capitals.

"What's happening in America is everyone's problem," Liz Chamberlin, a dual US-British citizen living in England told AFP at a London rally. "It's economic lunacy... He is going to push us into a global recession."

In Berlin, 70-year-old retiree Susanne Fest said Trump had created "a constitutional crisis," adding, "The guy is a lunatic."

In the US, a loose coalition of dozens of left-leaning groups like MoveOn and Women's March organized "Hands Off" events in more than 1,000 cities and in every congressional district, the groups said.

The unifying theme: the growing resentment of what another organizing group, Indivisible, has called "the most brazen power grab in modern history," led by Trump and his close advisor Elon Musk.

Trump has angered many Americans by moving aggressively to downsize the government, unilaterally impose his rightwing values, and sharply pressure other countries over borders and trade terms.

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"People here in the United States are really not cool with what's going on in DC right now," protester Rachael Nevins told AFP at a rally in New York.

Many Democrats are irate that their party, in the minority in both houses of Congress, has seemed so helpless to resist Trump's aggressive moves.

"The Democrat Party is kind of wimping out... and not actually standing up for our rights," said Abbott Sherwin (19), a college student from Raleigh, North Carolina, who was marching in Washington, adding that "the Republican Party is a cult around Trump."

Thousands of people convened on the National Mall, just blocks from the White House, to hear speakers including Representative Jamie Raskin, a Democrat who served as impeachment manager during Trump's second impeachment.

"They've woken up a sleeping giant, and they haven't seen nothing yet," activist Graylan Hagler (71) told the crowd. "We will not sit down, we will not be quiet, and we will not go away."

Saturday's demonstrations were peaceful. A festive atmosphere prevailed on a mild day in Washington, with protesters ranging from the elderly to young couples with infants in strollers.

A Women's March protest shortly after Trump's first election in 2016 drew an estimated half-million people to Washington. Organizers for the latest Washington rally had predicted a turnout of 20,000 but by Saturday afternoon said the number appeared considerably larger.

As Trump continues aggressively shaking things up in Washington and beyond, his approval rating has fallen to its lowest since taking office, according to recent polling.

But despite pushback around the globe to his sweeping imposition of tariffs, and bubbling public resentment, the White House has dismissed the protests.

The Republican president, still popular with his base, has given no sign of relenting.

"My policies will never change," Trump said Friday.