A number of people have been arrested on suspicion of offences including breaching the peace and conspiracy to cause public nuisance close to the coronation, Scotland Yard said.
Just Stop Oil protesters appeared be arrested on the Mall in London.
A large group were seen in handcuffs with police cordoning them off.
It comes after anti-monarchy campaign group Republic said its chief executive had been arrested along with five of his team.
It tweeted: “This morning, @GrahamSmith_ and 5 members of our team were arrested. Hundreds of placards were seized. Is this democracy? #NotMyKing #Coronation”
In a statement on Twitter, the Metropolitan Police said: “A significant police operation is under way in central London.
“We have made a number of arrests in the area of Carlton House Terrace.
“The individuals have been held on suspicion of breaching the peace.
“Earlier today we arrested four people in the area of St Martin’s Lane.
“They were held on suspicion of conspiracy to cause public nuisance.
“We seized lock-on devices.
“A further three people were arrested in the area of Wellington Arch.
“They were held on suspicion of possessing articles to cause criminal damage.
“There will be further updates later today.”