Thousands of activists have gathered in Trafalgar Square, outside the Houses of Parliament and by the US embassy to protest the death of George Floyd in the US, as well as acts of police brutality in the UK.
Protesters could be heard chanting "black lives matter" and "say my name, George Floyd" in central London, in reference to the campaigning civil rights group.
Others held up placards saying "Racism has no place" and "I can't breathe".
A vicar at St Martin-in-the-Fields church on Trafalgar Square, said she could see the crowds gathered for the protest from the church.
Reverend Sally Hitchiner told the PA news agency: “I’m very sympathetic to the issue but also surprised to see the strength of emotion that has gathered people together.
“It’s showing there are people in the UK who care passionately about the situation in the US.
The protesters did not appear to be following social distancing rules, she said.
But she added: "I think there’s a huge amount of passion there and that’s overriding their concerns.
“It’s an issue that requires passion but at the same time there’s a huge amount of risk in what they’re doing.”
The protest comes after an event in Peckham on Saturday and is set to be followed by several more in the capital next week.
The US has been rocked by five days of protest across many cities, after George Floyd, a black man, died in police custody this week in Minneapolis.
— Nick McAvaney (@nick_mcavaney)May 31, 2020
Many US protests have been peaceful, but others have turned into violent confrontations between demonstrators and police.
A teenage protestor in Detroit was shot dead by an unknown passerby, while a law enforcement officer in Oakland was also killed after being shot.
Around 1,300 arrests have been made, with 500 of those in California on Thursday.
President Trump has expressed his sorrow at the death of Mr Floyd, but hit out at protestors and threatened Washington activists with "vicious dogs" and ominous weapons" if they entered the White House.
Derek Chauvin has been charged with third-degree murder and manslaughter after he was filmed kneeling on Mr Floyd's neck for around eight minutes.
With protesters seemingly not keeping to social distancing rules, some people warned that such large crowds could help spread the virus.
One Twitter user said: "Not much social distancing, who would have thought we were in the middle of a pandemic.."
Separate group of several thousand marching from Parliament Square over Westminster bridge pic.twitter.com/JHeAuyjVmZ— Joe Goodman (@joegoodman94)May 31, 2020
It comes as officials in the US warned about the dangers of protesting amid the coronavirus pandemic.
The mayor of Atlanta, which has been hit by major protests, has warned demonstrators they have put themselves at risk of contracting coronavirus and should get tested.
And as emergency orders imposed at the start of the pandemic are lifted, protests have now been added to the list of concerns about a possible second wave of infections.
Similar issues have been raised in Paris and Hong Kong, where anti-government protesters have accused police of using social distancing rules to break up their rallies.