Scuffles broke out as police moved in on demonstrators in Trafalgar Square, who formed human blockades in an attempt to prevent arrests and initially forced officers to move back.
Demonstrators advanced on police while shouting “choose your side” and some were seen throwing objects at officers after a largely peaceful demonstration on Saturday afternoon.
At around 3pm, the Metropolitan Police announced that it would be dispersing protesters and making arrests after trying to “explain, engage and encourage them to leave throughout” the day.
Footage showed several lines of officers in riot gear near the National Gallery, with mounted police on standby.
“Protesters have remained, putting themselves and others at risk,” a spokesperson for the Metropolitan Police said.
“This, coupled with pockets of hostility and outbreaks of violence towards officers, means we will now be taking enforcement action to disperse those who remain in the area. Those who remain may get arrested.”
The Resist And Act For Freedom rally is the latest in a series of protests by a wide-ranging coalition of groups who oppose lockdown restrictions.
Supporters of the QAnon theory, which centres on claims that Satan-worshiping pedophiles are running a global child sex-trafficking ring, could be seen in the crowd.
Several people held up signs opposing vaccinations and 5G technology, while others waved St George’s flags.
The crowd cheered as a speaker told them that coronavirus was a “novel coronavirus, like a novel, like a story – it’s all made up”. Another woman claimed that 5G “grows cancer”.
One protester held a banner calling for the government's Sage scientific advisers to be sacked, while another's declared Covid-19 a “hoax”.
The protest had been advertised by organisers as an “medic-focussed event with expert speakers, NHS and police whistleblowers. Protecting our families, our elderly and our children”.
The speakers included high-profile conspiracy theorists who have been speaking at a number of similar rallies in recent months.
A lead organiser is a nurse whose registration was suspended by the Nursing and Midwifery Council in July for spreading false information about coronavirus and vaccines.
Other speakers included the chair of the right-wing Irish Freedom Party, a Republican politician from Minnesota and prolific anti-5G campaigner Mark Steele, who was jailed for shooting a teenage girl in the head in the 1990s.
It comes amid concern that the spread of disinformation on coronavirus and potential vaccines will worsen the pandemic.
Police had appealed for the public to adhere to restrictions and social distancing over the weekend, as some forces mounted extra patrols to enforce the law.
A further 16 people who tested positive for coronavirus have died in hospital in England, bringing the total number of confirmed reported deaths in hospitals to 29,735, NHS England said on Saturday.
Professor Neil Ferguson, whose modelling led the government to order the lockdown in March, urged ministers to act “sooner rather than later” as cases rise.
Boris Johnson is to consider new restrictions across England after the latest figures showed new infections doubling every week, with the R rate between 1.1 and 1.4.
“We are now seeing a second wave coming in. We are seeing it in France, in Spain, across Europe - it has been absolutely, I'm afraid, inevitable we were going to see it in this country,“ he said on Friday.
The “rule of six” came into force on Monday to restrict private social gatherings, but protests are exempt if they are organised in accordance with guidelines.
Ministers are thought to be looking at a temporary two-week ”circuit break“ in an attempt to break the chain of transmission.
The move could see pubs and restaurants ordered to close or face a 10pm curfew, while socialising between households could be banned.
Tougher new restrictions have already been imposed in large parts of England's north west, West Yorkshire and the Midlands.