Clashes have broken out between far-right protesters and police officers as the Metropolitan Police warned protesters they must leave central London by 5pm.
In an attempt to avoid a repeat of last week's violent clashes, authorities had told Black Lives Matter protesters to stick to their planned route near Hyde Park, while far-right groups were ordered to remain near Parliament Square.
Police officers blocked off all the exits to Parliament Square for a time on Saturday afternoon, causing demonstrators to jump a fence into the grounds of Westminster Abbey in order to leave.
Footage posted on social media shows far-right demonstrators throwing missiles and bottles at police, while others tried to jump over cordons to confront officers.
Among those taking part in the protests were members from Britain First and the Democratic Football Lads Alliance.
Members of the groups had vowed to protect memorials from being defaced after the Cenotaph and the Sir Winston Churchill statue were spray painted amid Black Lives Matter protests last weekend.
A group clashed with police close to the Cenotaph in central London, while some demonstrators were seen throwing bottles at officers close to Westminster Bridge.
WARNING: The video below contains strong language and violence
Sharing a video of demonstrators in Whitehall, London, clashing with police and throwing objects, Home Secretary Priti Patel tweeted: “(Thoroughly) unacceptable thuggery.
“Any perpetrators of violence or vandalism should expect to face the full force of the law. Violence towards our police officers will not be tolerated.
“Coronavirus remains a threat to us all. Go home to stop the spread of this virus & save lives.”
Police had feared anti-racism demonstrations - sparked by the death of George Floyd in the US last month - could be hijacked by counter-protesters.
Black Lives Matter called off their planned protest on Saturday to avoid clashes between the groups but police believe thousands will still attend.
Aerial footage shows clashes between protesters and police. This footage has no sound
Last week, dozens of arrests were made and 27 officers were injured.
This Saturday, those affiliated to the Black Lives Matter protests must remain north of the police carrier erected on Whitehall, while right wing protesters have been ordered to remain south of the line.
The conditions were set under section 12 of the Public Order Act.
There were also planned protests in Brighton, Newcastle, Bristol, Cardiff and other towns and cities across the country in support of Black Lives Matter.
On Friday, statues in Parliament Square including Winston Churchill, Nelson Mandela and Mahatma Gandhi were boarded up to prevent them being targeted by either side.
Met Commander Bas Javid, brother of former chancellor Sajid, said he understood the depth of feeling of protesters, but asked people not to come to London while shutdown rules are still in force.
“If you were planning to come to London, I again would urge you to reconsider, but if you are still intent, please familiarise yourself with what the conditions are,” he said.
“Please keep yourself safe by complying with government guidance on social distancing.”
Anti-racism group Hope Not Hate has said football gangs from West Ham, Chelsea, Millwall, Sheffield Wednesday, Hull and Spurs are among the groups planning on coming to London.
On Friday, the Prime Minister expressed his dismay at the growing focus on removing statues in the wake of the toppling of slave-trader Edward Colston in Bristol on June 7.
More than 60 other statues are now listed as targets on a website called Topple the Racists.
The Prime Minister said to take statues down would “be to lie about our history”.
Boris Johnson, in a series of social media posts, said: “We cannot pretend to have a different history.
“Those statues teach us about our past, with all its faults.”