Violence that broke out during a "Kill The Bill" protest was caused by people who "came for a fight with police", Bristol's chief constable has said.
The event was organised to protest against the government's Police, Crime, Sentencing and Courts Bill that would increase police powers to deal with non-violent demonstrations.
However, what started out peacefully on Sunday afternoon turned ugly after hundreds of protesters marched from College Green to the New Bridewell police station.
Twenty police officers were injured, two seriously, with one suffering broken bones and another with a suspected punctured lung, during violent skirmishes with masked thugs.
Andy Marsh, of Avon and Somerset Police, told Sky News a number of those protesting "came for a fight with the police".
"It was a terrifying scene. Neighbourhood officers were effectively trapped inside the building with people on the roofs throwing fireworks at them, hurling projectiles.
"And the other officers outside doing their very best to protect everyone present.
"It really was a disgraceful scene committed by criminals. I don't believe this was a protest.
"It wasn't people frustrated with the lack of ability to protest - this was people intent on causing serious disorder, violence and damage, people with a grudge against policing.
"The people involved in assaulting the officers, burning out vehicles, damaging vehicles, smashing windows, hurling projectiles from the multi-storey car park, throwing things at our horses and dogs - they were people who came for a fight with the police.
"We did everything that we could to try to calm the situation… to disperse that crowd to encourage them to leave but ultimately it unfortunately turned to violence."
Rioters smashed the windows of the police station and also destroyed police vehicles parked nearby, setting fire to a car and a van.
Cars parked in a multi-storey car park next to the police station were also damaged by protesters.
Bristol's mayor Marvin Rees said he had "major concerns" about the bill, but condemned the violence.
He told Sky News: "I'm furious. It's the level of political illiteracy of these thugs which is really a problem here.
"How will what they did yesterday lessen the likelihood of this bill going through?
"What they have done will just be put in the evidence bag of those who want the bill to go through.
"They will also increase the likelihood of people in communities that have been on the rough end of the criminal justice system, remaining on the rough end of the criminal justice system."
Boris Johnson has described the violent scenes that marred the protest as "unacceptable".
Speaking to broadcasters at BAE Systems in Preston, the prime minister said: "I think all that kind of thing is unacceptable and the people obviously have a right to protest in this country.
"But they should protest peacefully and legally."
Sue Mountstevens, police and crime commissioner for Avon and Somerset, said seven people had been arrested so far and there would be "many more" detained.
"It's disgraceful and outrageous.
"There will be warrants, there will be arrests and police will be checking on the CCTV. There will be further arrests in the next few hours and days."
Six people have been detained for violent disorder and a seventh held for possession of an offensive weapon.
One protester told Sky News: "I think it was important to be down here when things are peaceful because the right to protest is crucial to any democracy obviously.
"This however, is a little bit embarrassing for the city of Bristol.
"This is not a peaceful protest. It's just going to be used against us as evidence to keep our right to protest away from us."
Shadow home secretary Nick Thomas-Symonds condemned the "appalling" and "completely unacceptable" violence in Bristol.
He told the BBC news channel: "Of course, I agree with legitimate protest in a COVID-safe and secure and peaceful way - that is one of the things that is most precious about our democracy - but there is no link between that and the appalling scenes that we saw last night."
The Police, Crime, Sentencing and Courts Bill would give officers in England and Wales more power to impose conditions on non-violent protests, including those deemed to be too noisy or a nuisance.
Those convicted under the proposed legislation could face a fine or jail.