Antimonarchy protesters booed the moment King Charles III was crowned in Westminster Abbey, before launching into a chant of "not my king".
It comes after a man with an unused megaphone has been arrested in St James's Park, with police claiming it could "scare the horses".
Police were seen surrounding a handcuffed protester at the park in London, with Sky's Jason Farrell reporting that an officer said he "was in a crowd of monarchists and [the megaphone] could cause them distress".
It was the latest in a series of arrests in the hours leading up to the King's coronation, with members of Just Stop Oil (JSO), Animal Rising (AR) and Republic being arrested. Human rights organisations have accused officers of being heavy-handed in their approach and one campaign group called it a "totalitarian crackdown".
Sky News reporters on the ground say more than a dozen have been arrested - and the Metropolitan Police have confirmed seven arrests so far.
Among those detained are the leader of anti-monarchy group Republic, who was led away in a police van just after 7am as he made his way to a designated protest site, and Just Stop Oil protesters who were arrested on the Mall near Buckingham Palace a short while later over their plans to go over the barrier.
But JSO claims they 20 members have been arrested merely for "wearing t-shirts" and disputes claims they had planned to jump the barrier.
AR said a number of their supporters were also arrested this morning whilst at a nonviolence training, miles away from the coronation. The group has confirmed on multiple occasions that it would not target the day's events.
Nathan McGovern, a spokesperson for the AR, said: "This is nothing short of a totalitarian crackdown on free speech and all forms of dissent. Just Stop Oil, Republic, and Animal Rising have experienced the true character of this Government's attitude towards peaceful protest today.
"We are sleepwalking into fascism and it is every single person's responsibility to stand up and say 'no more'."
Read more:
Meet the coronation protesters
'Dystopian nightmare'
Footage on Twitter shows a police officer taking the details of Republic CEO Graham Smith.
In the video, one officer can be heard saying: "They are under arrest, end of."
Scotland Yard said four people have been arrested on "suspicion of conspiracy to cause public nuisance", after they were found with lock-on devices. A further three people were arrested at Wellington Arch and are being "held on suspicion of possessing articles to cause criminal damage".
A spokeswoman for JSO said five demonstrators were also arrested at Downing Street.
She said the group's plan was "only to display T-shirts and flags", adding: "This is a dystopian nightmare."
Onlookers to the arrests at The Mall sang the national anthem as the demonstrators shouted messages about climate change and the right to protest.
Some people approached protesters who were wearing handcuffs and told them to "shut up", while others heckled the group and laughed at them.
'Worrying' use of new powers
Republic activist Luke Whiting, 26, said the group was arrested as they tried to bring yellow placards to a protest, and questioned if it was because "one of them was carrying a megaphone".
He told Sky News: "We were very open with police about what we planned to do, which is hold a demonstration in Trafalgar Square.
"It seems [the protesters] have been arrested using this new powers. It's quite a worrying thing to happen, we were pretty shocked."
He said the group has been "open" with the police about what they had planned.
"They've said it's perfectly legal for us to bring placards, bring flags and protest the coronation," he added. "In a democratic society it is absolutely our right to do this and be peaceful and that's what we are planning to do."
'Incredibly alarming'
Non-profit campaign group Human Rights Watch said the "incredibly alarming" arrests were "something you would expect to see in Moscow, not London".
Its UK director Yasmine Ahmed said in a statement: "Peaceful protests allow individuals to hold those in power to account, something the UK government seems increasingly averse to."
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On Wednesday, the Met announced it would have an "extremely low threshold" for protests during the coronation, and demonstrators could expect "swift action".
The policing operation is set to see 11,500 police officers on duty on Saturday.
Sacha Deshmukh, Amnesty International UK's chief executive, said the human rights group was concerned about the force's statements about its "low tolerance" for protests ahead of the arrests.
He said: "We need to see what details emerge around these incidents, but merely being in possession of a megaphone or carrying placards should never be grounds for a police arrest."
Police 'found evidence of locking on'
One woman in a Republic T-shirt who was arrested said the group had been questioned about how they got through road closures.
"We had a delivery of placards ready for the protest, and then the tactical support unit questioned us as to how we had got through the road closures," she said.
"They questioned whether what we were doing was a delivery. They then said they found evidence of means of locking on, of items that could be used to lock on, and they arrested us."
Officers carried her away from where she had been standing outside a Tesco store, while two men who appeared to have been part of the same demonstration were carried away by officers into a marked police van.
Why protesters have taken to the streets
Campaigners from two anti-monarchy groups have been speaking to Sky News this morning, ahead of the coronation ceremony, about why they have taken to the streets.
"I don't believe that power should pass from one nepotism baby to the next," said Imogen McBeath from No More Royals.
"There is no qualification that they have that means they have a divine right to rule."
When questioned about the King's attempts to slim down the monarchy, she replied: "If they wanted to make an effort, they would recognise where their wealth comes from - which is colonisation.
"They would give back jewels and artefacts that they have stolen."
Luke Whiting from Republic added: "It's an incredibly expensive coronation process, up to a quarter of a billion pounds in the middle of a cost of living crisis. I think people have really been shocked by that."
