"Stand united, we will never be divided," was the message chanted by the crowd as people marched through central London.
Cheers erupted every few minutes as the crowd held up placards to the beat of drum and bass music from a portable sound system.
"Girls just wanna have fundamental rights", "Women won't be trumped" and "Burn bras not bridges" were some of the messages directed at US President Donald Trump from the UK.
Women - and men - of all ages descended on the capital for the Women's March in London on the first full day of his presidency.
There was a united message from the crowd, who came with glitter on their faces and even fancy dress to take part in the two-mile walk.
Many were parents who said they wanted to send out a message for the next generation that they have a voice and can stand up for the women's rights they believe to be under threat from the new US administration.
Mum-of-one Danae Savvidou, 25, travelled alone from Gloucestershire to London to take part in the event for the sake of her 10-month-old daughter.
She said: "She was born during the presidency of a man who openly supported women's rights and protected them.
"I feel like we've gone back 100 years and I feel sad for her generation.
"Donald Trump isn't presidential material. He's openly misogynistic and racist as well. I see America as a leader and partners in the Western world. He represents such a big nation.
"Our leaders over here are right wing as well. It's not going the right way for me.
"Brexit is a concern. I hope we protect the rights the EU offers, such as employment rights and maternity. These issues need to be spoken about. When a nation is doing badly, women suffer.
"Personally I want my daughter to see what I've done today to show you can do things to change the world and she does have the power."
It was a message which resonated with many other parents as they walked with their children in the fresh winter's air along Piccadilly.
Nancy Pegg, 39, a mum-of-two from south-west London, came along with her daughter Sophie, nine, who carried a yellow banner emblazoned with the words "Yes to equality".
She said: "This is about equality for girls not in a fortunate position.
"Trump is a concern but empowering women is the main motivation. I think it's important for my daughter to have a powerful voice and to know she can be a strong force.
"We live in a male-dominated world. I want to show her anything her brother can do, she can do too. There are no boundaries."
Although the event was labelled a Women's March, there were hundreds of men in the crowd showing their support.
Car horns beeped to galvanise the demonstrators who, in turn, greeted the drivers with cheers as the march progressed to its rally in Trafalgar Square.
The Raise Voices Choir motivated the protesters by singing "Don't let Trump get his way" to their own version of "The Battle Hymn of the Republic".
Student Patrick Bone, from Shepherd's Bush, London, attended because he felt "progress made in the last decades is in threat of being eroded".
He added: "Trump's election signalled a rise of the populist right who look to blame economic problems on minorities or disenfranchised groups.
"His election was a catalyst for something that's been coming a long time.
"This march is to show we will stand and be counted. This is only the beginning. The work begins today."
Tom Amies, 33, a doctor from Middlesex, walked beside his wife Lydia, 34, as he carried their 11-month-old daughter Niamh in a baby carrier sling.
"This is for my daughter, he said.
"There has been a political slide to the right and a sense of misplaced trust. Trump wants to repeal Obamacare. It shows how good we have it with the NHS.
"There are going to be people there who have that healthcare for life-saving treatment and they will no longer be able to afford it."
The demonstration brought representatives from all nationalities, including Americans who felt they needed to take a stand even though they were thousands of miles away from their country.
Retired banker Carol Moore, 68, originally from New York, came to represent the Democrats Abroad UK Women's Caucus.
She said: "I've come because of the horror of seeing Donald Trump win. He is divisive and will hurt the middle classes by repealing the healthcare act.
"This march has taken on huge visibility here in the UK because the issues are global. Women's pay was an issue when I worked in the City.
"There is still the issue of sexual violence and how it's prosecuted and handled here.
"I hope this is a message to women to recognise they have a voice to fight issues here in the UK and around the world."
Business development manager Anna McDermott, 29, originally from California, has been in the UK for 11 years.
She said: "As an American, I cannot accept what Donald Trump says and I can't accept him as a president.
"I do hope this sends out a message. 'Good morning. Welcome to day one of the resistance. This is the world shouting back'."
As the crowd moved into Trafalgar Square, the noise quietened so demonstrators could listen to the speakers on the stage, who included TV presenter Sandi Toksvig and Labour MP Yvette Cooper.
However, the final address was given by 10-year-old Sumayah Siddiqi who read out a poem to the crowd which had a message of optimism with the words "I shall stand for love".