LONDON — If President Donald Trump was in any doubt about the welcome he would receive from the public during his visit to Britain, the sheer scale of people marching against him through London on Friday afternoon would have told him everything he needed to know.

On Thursday, shortly after arriving, he had claimed: "I think they like me a lot in the U.K."

Tens of thousands of Brits took to the streets to contradict his assessment. Dozens of anti-Trump demonstrations kicked off across the United Kingdom Thursday, and will continue through the weekend.

"I think that's a hard argument to sustain after today," John Rees, co-founder of Stop the War Coalition and one of the organizers of the Friday's largest march, said of Trump's comment. "This is a vast expression of political opposition."

The largest of two marches through central London Friday culminated in a huge rally in Trafalgar Square, which was nearly completely packed with people by late Friday afternoon. London's Metropolitan Police would not comment on the crowd's size but organizers told NBC News that about 250,000 people attended.

"The one thing you can say about the president of the United States is he is an equal-opportunities hater," said Rees. "He hates broadly and inclusively. He dislikes women, he dislikes refugees, he dislikes immigrants, he dislikes Muslims, he dislikes a lot of working people. So it's not very surprising there's a broad coalition in opposition to him."

That rally began moving 45 minutes later than planned, with surrounding roads being too full of protesters and police attempting to clear them. The march then proceeded to Trafalgar Square, which saw political speakers and musicians address the crowd at the packed rally.

Organizers asked those in the square to move forward in order to allow more of those marching to file in shortly before the opposition Labour party leader Jeremy Corbyn took to the stage to address the crowd.

“We are asserting our right to demonstrate, our right to free speech and our right to want a world that’s not driven by misogyny, racism and hate,” Corbyn told the massive crowd.

The event was organized by a collection of largely left-wing groups and activists operating under the banner of the Stop Trump Coalition.

The even larger Stop Trump Coalition march is ready to start in Langham Place. It’s already ferociously noisy and full of Dump Trump banners pic.twitter.com/1ng89zexao — Alastair Jamieson (@alastairjam) 13 July 2018

Kim Nelson, a 25-year-old refugee charity worker, was one of the Londoners who turned out for the protest. He told NBC News he said the size of the rally sends a "powerful message."

"It's a message that we shouldn’t just let Trump say all these things, or do all these awful things without a sense of accountability," he said.

Kim Nelson, a 25-year-old refugee charity worker from London. Alexander Smith / NBC News

"I was trying to get a sense of how many people here, and it’s better than I thought," Nelson added. "There’s people all over coming."

The president has decided to largely avoid London during his trip, perhaps mindful of being confronted or associated with a mass display of public rejection. But the demostrations will not be confined to the capital.

Among the 68 events listed on the Stop the Trump Coalition website is the "Orkney Picnic of Resistance" in the isles in northern Scotland, and the "Anti-Trump Vigil" in the Welsh capital of Cardiff.

A earlier protest in Central London featured a 20-foot blimp in the shape of an orange baby with Trump's face floating above the Houses of Parliament.

Friday's central London marches began with the smaller, women-led Bring The Noise demonstration, where several thousand people carried orange and pink placards and balloons with slogans including “Dump Trump” and “Stop Trump.”

Chants drowned out the sound of helicopters overhead, as hundreds of police waited and watched from side streets.

Teacher Ruth Coles, 37, was among those gathering at the start of the rally with her daughters Isla, 5, and Aisling, 7 months.

Ruth Coles, 37, and her children Isla, 5, and Aisling, 7 months. Alastair Jamieson / NBC News

“It’s my first demonstration. My friend goes to protests a lot and she said that when ordinary people start protesting, you know it’s time for things to change," Coles said. “I want to show that it’s good to be a girl.”

Miatta Marke, 43, has also come to the march with her daughter, Ambah, 17.

“This is a reaction against the misogyny that’s evident in everything his administration does,” Miatta said. “I thought it was important to bring my daughter today so we could be on the right side of history and not just screaming at the television.”

Ambah said that Americans needed to “wake up and realize we can’t let someone like Trump control our policies and control the way we view the world.”

Gracie Dahl at Friday's Bring The Noise protest in London. Alexander Smith / NBC News

“What have I got against Trump? What haven’t I got against him?” said Gracie Dahl, 19, an illustration student from London. “His views on women, refugees, separating children from their families, he’s just a generally abusive, arrogant man and I can’t stand he’s been given the platform he has.”

She added: “America can keep him if they like him so much but we don’t want him here.”

Workers, shoppers and tourists had to stand aside as the marchers moved down Regent Street — which is home to many high-end stores and is already in one of the busiest areas of the city — to make way for the thousands of deafening protesters banging drums and blowing whistles.

Carolyn Royan, 48, a Texas-born opera singer who has lived in London for 20 years, held aloft a banner that read “Texans against Trump.”

They were asked to #BringtheNoise and they did! It’s deafening on Regent Street pic.twitter.com/jVjaaMUUc9 — Alastair Jamieson (@alastairjam) July 13, 2018

“This is my first ever protest,” she said. “I am sick and tired of having a lying, bigoted misogynistic racist as a president. He cares nothing for ordinary Americans and is simply out to enrich himself and his family.”

As the march progressed, protesters started chanting: “Donald Trump, go away, racist, sexist, anti-gay.”

Adding to the heated conversation around Trump in the U.K., an interview with British tabloid The Sun was published late Thursday in which Trump trashed Prime Minister Theresa May's Brexit negotiations and warned she may have blown a trade deal with the U.S.

Protests began even before that interview was published. Marine One thundered into the London sky Thursday night, while several hundred protesters gathered below to raise a din with pots, pans, drums, horns, whistles, and megaphones and held placards with messages of varying profanity.

Their message was chanted over and over. "F*** Trump, F*** Trump, F*** Trump," they yelled, all the while making a din with their improvised instruments.

The protest was held at a temporary security fence around the U.S. ambassador's Winfield House residence, where Trump is staying during his four-day visit.

Trump flew by helicopter from the ambassador's residence to Winston Churchill's ancestral home, Blenheim Palace, in Oxfordshire on Thursday evening.

There, he and first lady Melania Trump attended a welcome ceremony and a lavish, black-tie dinner by May, her husband, Philip, and a host of business leaders.

At both Winfield House and Blenheim Palace Thursday, they were also greeted by protest. When their helicopter left the former, the pandemonium almost drowned out the rotor blades.

"He's creating and fomenting a culture of racism, misogyny, intolerance, hatred and negativity and it's very dangerous," said Kate Gartside, 54, a screenwriter from London. She held a sign reading: "Lock him up!"

"The feeling of the British people has manifested itself here today," said her husband Rod Rawley, 72, also a writer and originally from California, shouting to make himself heard over the cacophony.

Really is rather loud. pic.twitter.com/3gtDmWFNQ4 — Alexander Smith (@AlexanderSmith) July 12, 2018

He added the anti-Trump demonstrations "will prove the number of people who are totally against what Trump stands for... Although I don't think he stands for anything apart from himself."

The protesters had a range of grievances, from Trump's remarks about Muslims and women, to his record on immigration, climate change and what organizers call his family's "corporate greed."

Some said they planned to stay all night at the fence, a good 200 yards from the residence, banging and hooting in a bid to keep the president awake.

Ashley MacDonald is originally from Columbus, Ohio, and has lived in the UK 16 years. This sign was conceived and painted by her 11-year-old daughter, who couldn’t come to the protest today but was aparently adamant to have a voice here. Those are her hand prints. pic.twitter.com/HiJiUUGJ16 — Alexander Smith (@AlexanderSmith) July 12, 2018

"It's embarrassing, isn't it?" said Jasmin Harper, 27, an insurance worker who moved from Virginia to London four years ago. "I'm appalled and disgusted by everything Trump does."

Marlon Kameka, 29, an actor, added: "As a black man, I don't like the way he's spoken about the NFL players, calling them 'sons of bitches,' or for him to say there were 'some very fine people' at the Charlottesville march. We still have issues around race in this country but it pales in comparison to America."

This is Dd Davies, a fine-art student from Hampshire who’s used her creative skills to make an electronic “effigy” of Donald Trump. “If he’s going to grab women by certain parts of their anatomy then I’m going to stab him in his y-fronts with a pin” pic.twitter.com/4uxZDGuLOL — Alexander Smith (@AlexanderSmith) July 12, 2018

Trump has spent much of Friday with May at the prime minister's Chequers country home, where the pair held a joint press conference. Later, he was due to meet with Queen Elizabeth II at Windsor Castle, before traveling to Scotland where he will visit at least one of his golf resorts.

A demonstration was planned for Glasgow’s George Square on Friday night and a mass rally in Edinburgh, starting at the Scottish Parliament and ending at The Meadows park, on Saturday afternoon.

Smaller protests were expected early Saturday at Balmedie in Aberdeenshire, where Trump has a new purpose-built hotel and golf course, and at Turnberry in Ayrshire.

Today’s ⁦@EveningStandard⁩: after Trump slags off London, the NHS and immigrants to our shores we say ‘No, Mr President” pic.twitter.com/RlxPkIUdR3 — George Osborne (@George_Osborne) July 13, 2018

These demonstrators don't appear to be just a vocal minority.

On Thursday, a poll by YouGov said fewer than one in five Brits had a favorable opinion of the president.

The same poll found 74 percent of respondents think Trump is a sexist and 63 percent think he is a racist. On the flip side, 38 percent think the president is a strong leader, 25 percent believe he is charismatic and 16 percent said he was honest.

Even before this week, Trump had threatened a frosty relationship with Britain and May.

He has slapped tariffs on British steel and aluminium, criticized the country's response to terror attacks, and appears to have warmed again to Russian President Vladimir Putin after a chemical attack that the U.K. blames on Moscow.

Trump also rubbed salt in the wounds of England's bitter World Cup defeat at the hands of Croatia on Wednesday night, telling a Croatian journalist on Thursday: "Congratulations, by the way."