Ten people have been arrested after anti-lockdown protesters clashed with police as they tried to shut down a huge demonstration in central London.
Missiles were thrown at police amid efforts to disperse thousands of people - many claiming coronavirus is a hoax. Four officers have also been injured, police say.
Officers penned the crowd in and water was thrown at them by demonstrators while crowds chanted "pick your side".
Bottles were thrown and police used batons against protesters, leaving some with visible injuries.
The Metropolitan Police said crowds at the demo in Trafalgar Square had "not complied" with social distancing rules. Ten arrests have been made and four police officers injured, including two who required hospital treatment, they said.
Demonstrators have been asked to leave and the force warned that anyone who stays could be subject to enforcement action.
In a statement, the Met said: "Crowds in Trafalgar Square have not complied with the conditions of their risk assessment and are putting people in danger of transmitting the virus.
"This has voided their risk assessment and we have informed the event organisers they are no longer exempt from the regulations.
"We are now asking those in Trafalgar Square to leave. Officers will be engaging with crowds and informing them of this development.
"By leaving now, you can keep yourself safe and avoid any enforcement action being taken by officers."
Mayor of London Sadiq Khan called the violence "unacceptable".
On Twitter, he said:
"This is unacceptable. Violence of this kind towards officers will not be tolerated and perpetrators will feel the full force of the law.
"I urge all protestors to leave now. Large gatherings are banned for a reason - you are putting the safety of our city at risk."
The protest has been held despite the fact that the UK's Covid-19 death toll hit 41,936.
Jeremy Corbyn's brother Piers, a known anti-vaxxer and conspiracy theorist, was seen amongst the crowds.
Thousands of people began yelling 'freedom' as speakers left the stage.
The meeting, which has been dubbed the 'We Do Not Consent' rally, had been set to move to Hyde Park later.
A website promoting the rally said: "We are campaigning to stop parliament renewing the Covid-19 oppressive legislation.
"We are fighting against the government's Covid policies which cause illness and death - and fighting for Action to cut claimed virus illness and SAVE LIVES."
The protest comes a week after a separate event which saw more than a dozen officers injured when a "small minority" targeted police and more than 32 arrests were made.
The Met said it had been engaging with organisers throughout the week to remind them of their legal obligations and explaining the events could be in breach of coronavirus regulations.
In a statement, they said:
"Ten people have been arrested following demonstrations in Trafalgar Square, which moved to Hyde Park.
Sadly, four of our officers have been injured, two require hospital treatment. We continue to urge crowds to disperse. This protest is no longer exempt from the regulations."
While protests are exempt from the "rule of six" in England, organisers must submit a risk assessment and comply with social distancing.
