Rioting erupted Friday evening in Sunderland, northeast England, where police said officers faced "serious and sustained levels of violence", the latest unrest linked to a mass stabbing earlier this week that killed three young girls.
Eight people were arrested and three officers required hospital treatment following hours of "utterly deplorable" disturbances, Northumbria Police Chief Superintendent Helena Barron said.
Two officers remained in the hospital early Saturday, she added.
Footage broadcast by the BBC showed a mob of several hundred rampaging in Sunderland's city centre, attacking police and setting fire to at least one car and a building next to a police office.
Keep Reading
- Day out with the trash trackers of Mukuru slums
- Haemophilia: Unveiling the bleeding disease
- Lukoye Atwoli calls for increased investment in brain, mental health research
- Puzzle of small village riddled with cancer
Other images shared on social media showed balaclava-clad youths throwing bricks and other missiles as fireworks and flares were let off.
"The shocking scenes we have witnessed in Sunderland this evening are completely unacceptable," Barron said, adding the "disorder, violence and damage" seen "will not be tolerated".
"A full investigation is now underway to identify anyone else responsible" in addition to the eight people arrested, she added.
The disorder came as police nationwide prepared for planned far-right rallies and other demonstrations this weekend, after two nights of unrest in several English towns and cities in the wake of Monday's knife attack.
London's Metropolitan Police said it had a "proportionate and risk-based" plan for rival pro-Palestinian and anti-immigration protests Saturday. Its officers arrested 111 people as a rally in Westminster turned violent late Wednesday.
But Friday night's disturbances in Sunderland, after a calm night nationwide Thursday, were an ominous sign for the coming days.
'Deeply anxious'
Responding to events there, Interior Minister Yvette Cooper vowed rioters will "pay the price for their violence and thuggery". She gave police "the full backing of the government to take the strongest possible action and ensure they face the full force of the law".
"They do not represent Britain," Cooper said.
Earlier, Merseyside Police said extra officers had been deployed in and around Liverpool city centre "to help prevent disorder or criminality" there. Despite a minor skirmish near a mosque, the evening passed off peacefully.
Liverpool lies close to the seaside town of Southport where Monday's knife attack occurred.
Far-right elements have been blamed for the disturbances in the aftermath of the stabbing spree targeting children at a Taylor Swift-themed dance party.
Officials have said online disinformation about the British-born 17-year-old suspect Axel Rudakubana helped fuel the unrest.
He faces murder and attempted murder charges over the stabbing rampage that also left five children and two adults critically wounded.
Police have said the case is not being treated as terror-related but have not revealed a motive.
Anger over the tragedy has fused with growing anti-immigration sentiment on the right of English politics, pushed by openly Islamophobic far-right figures.
After the violence in Southport late Tuesday, unrest rocked the northern cities of Hartlepool and Manchester as well as London 24 hours later.
In Southport, the mob targeted a mosque, prompting hundreds of Muslim places of worship across the country to step up security amid fears of more anti-Islamic demonstrators.
Faith leaders say mosques have been hiring paid security staff and checking their CCTV cameras are working.
"The Muslim community is deeply anxious right now," Zara Mohammed, secretary-general of the Muslim Council of Britain, told AFP.
'Sow hatred'
Prime Minister Keir Starmer has accused "thugs" of "hijacking" the nation's grief to "sow hatred" and pledged that anyone carrying out violent acts will "face the full force of the law".
In power for less than a month, Starmer met Friday with local leaders in Southport to discuss "a package of support for the local community", his Downing Street office said.
Starmer's visit came the day after he announced a new "national capability" to tackle disorder in the wake of the recent disturbances.
The new measures will allow the sharing of intelligence, wider deployment of facial-recognition technology and criminal behaviour orders to restrict troublemakers from travelling.
The police alert for the weekend comes after far-right social media channels advertised "enough is enough" anti-immigrant rallies and anti-fascism groups vowed to stage counter-protests.
"Enough is enough" has emerged as a rallying online slogan for the far-right and others following Monday's attack.
South Yorkshire police said Friday they knew of a planned protest in the town of Rotherham, while officers in south Wales said they were preparing for events being planned for Saturday in Cardiff.
Police in Northern Ireland noted social media posts calling for roadblocks "using women and children", as well as a march to an Islamic centre in Belfast on Saturday.