Here's what's happening:
- Donald Trump has become the 45th president of the United States after taking the oath of office in Washington DC on Friday.
- A range of protests connected to Trump's inauguration are taking place in London and across the UK as he becomes president.
- Thousands are due to attend a series of women's marches – open to everyone – in London and elsewhere in the country on Saturday, in solidarity with a march in Washington a quarter of a million people are expected to join.
- Keep up to date with events in the US here.
Organisers have estimated that around 100,00 people were at the march in London.
The rally finished at approximately 3pm and by then crowds had begun to disperse.
Speakers at the rally included Labour MP Yvette Cooper.
A rally took place at the end of the march in Trafalgar Square.
Talking to the crowd, she said, "When the most powerful man in the world says it's okay to sexually assault women because you are rich and powerful, we have to stand up and say no way."
Trafalgar Square was closed off as it reached its maximum capacity.
Despite the rally starting, people were still marching and had been unable to enter Trafalgar Square for the rally.
The march's organisers say 80,000 people have joined the London protest
Marchers make their way through the streets of London
Sections of the march have now reached Trafalgar Square, where a rally will take place.
The Women's March on London has now begun
Thousands of people have now begun marching towards Trafalgar Square.
If you are not on the march, you can follow a live-stream of it here.
– Ikran Dahir
Thousands of women and men will take to the streets of Britain on the first day of Trump's presidency
The biggest march in the UK will take place in London, beginning outside the US embassy before a rally in Trafalgar Square.
The London protest's organisers say they are marching "for the protection of our fundamental rights and for the safeguarding of freedoms threatened by recent political events. We unite and stand together for the dignity and equality of all peoples, for the safety and health of our planet and for the strength of our vibrant and diverse communities."
Embassy protesters chanted "Donald Trump has got to go".
Singer Lily Allen was among those at the protest.
She performed a song for those at the embassy. Protesters joked that Trump couldn't get A-list performers for his inauguration but they had managed.
Protesters then marched from the embassy across central London.
People at the embassy protest told us why they were there
You can see more pictures here.
– Ikran Dahir
People are demonstrating outside the US embassy in London
People are gathering outside the US embassy in London to protest against newly-inaugurated president Donald Trump.
– Ikran Dahir
Anti-Trump protest banners were revealed earlier today
Protest banners were dropped from bridges in London this morning as part of the Bridges Not Walls project.
More than 150 banners are being unfurled across the world, including in the US, Ethiopia, Norway and Australia.
Read more about the protest here.
– Matthew Tucker
The protests taking place this weekend
Stand Up to Racism has organised over a dozen anti-Trump protests in the UK today, the biggest of which will take place outside the US embassy in London as Trump is sworn in.
Shadow cabinet members Emily Thornberry, Clive Lewis, and Diane Abbott are among more than 50 public figures to have signed a joint statement calling on "everybody of goodwill" to join protests against the new president on the day of his inauguration.
"There is a link between inflammatory statements by politicians and racist attacks and hate crimes on the street," shadow home secretary Abbott said this week.
"There has been a rise in such crimes in Britain following the EU referendum and a similar pattern has emerged in the US. Now is the time for people of goodwill to unite and stand up to racism."
Saturday's Women's March on London is taking place in solidarity with similar events being held in more than 60 countries, including the US. Thousands of women and men are expected to march from the US embassy to a rally in Trafalgar Square.
London-based artist Emma McNally, one of the founders of the London protest, told BuzzFeed News that the election of Trump was a catalyst for the march.
She said 2016 had been a "very dark year": "It was marked by rhetoric that stoked division. When Trump was elected it felt like a tipping point."
McNally said the idea for the London protest was founded in the days after the election, in solidarity with the march that would take place in DC.
"The time to come together is right now," she said. "He's a catalyst, he's just one man, elected because of social conditions."
Anti-racism group Hope Not Hate is among those supporting Saturday's march. A spokesperson said the group was "not 'protesting' against Trump per se", but calling on people to "put compassion back at the heart of our politics".
'We are calling on people to respond to Trump's message of fear and division by building bridges between, and within, communities," the representative said.
The Women's Equality party, which says it is one of the main partners of the march, said: "It is time that women and men unite and organise against the intolerance, divisiveness, misogyny, and racism that characterised 2016's key votes in the UK and the US."
– Matthew Champion