The Metropolitan Police has threatened to shut down a number illegal raves planned in London on Saturday.
In a statement, the force warned that unlicensed music events (UMEs) "remain illegal" and that officers will "take action" against organisers.
Anyone organising an illegal rave, unlicensed music event or any other type of gathering of more than 30 people can be fined up to £10,000 under coronavirus legislation.
Earlier this month officers broke up an illegal party with 150 people at a derelict pub in the Docklands.
Scotland Yard also urged anyone attending protests and events in the capital to "stick to the rules".
A number of protests will be taking place simultaneously in London on Saturday, including an anti-lockdown protest involving conspiracy theorist David Icke, a protest against US President Donald Trump, and a protest over the detention of demonstrators in Hong Kong.
Commander Ade Adelekan, Gold Commander for Saturday, warned that protests may not be exempt if organisers do not comply with the rules.
“As Covid-19 cases rise across the capital, it is vitally important for us all to stick to the regulations which are there to keep everyone safe", he said. "Throughout London, we will have officers on hand to respond to reports of breaches but to also engage with communities on the rules.
“I would urge those looking at attending a protest tomorrow that these events may not be exempt from the regulations if the organisers do not comply with the regulations and submit a satisfactory risk assessment. This could result in crowds being dispersed or indeed enforcement action being taken by officers on scene.
“Everybody has a personal responsibility to stick to the regulations and help prevent the transmission of coronavirus. We will not allow the health of Londoners to be put at risk and officers and we will take action against those groups or individuals who flagrantly and dangerously breach these rules.”
Protests are exempt from the ban on gatherings of more than six outdoors.
However, the organiser must carry out a full risk assessment and take steps against preventing transmission of the virus.