Authorities in Northern Ireland are seeking to restore calm after Protestant and Catholic youths in Belfast hurled bricks, fireworks and petrol bombs at police and each other.
It was the worst mayhem in a week of street violence in the region, where the UK's exit from the European Union has unsettled an uneasy political balance.
Crowds including children as young as 12 or 13 clashed across a concrete "peace wall" in west Belfast that separates a British loyalist Protestant neighbourhood from an Irish nationalist Catholic area.
Police fired rubber bullets at the crowd and nearby a city bus was hijacked and set on fire.
Northern Ireland has had sporadic outbreaks of street violence since the 1998 Good Friday peace accord ended "the Troubles" - decades of Catholic-Protestant bloodshed over the status of the region in which more than 3000 people died.
But Police Service of Northern Ireland Assistant Chief Constable Jonathan Roberts said Wednesday's mayhem "was at a scale we have not seen in recent years".
He said a total of 55 police officers had been injured over several nights of disorder and it was lucky no one had been seriously hurt or killed.
Brexit has highlighted the contested status of Northern Ireland, where some people want to stay part of the UK while others see themselves as Irish and seek unity with the neighbouring Republic of Ireland, an EU member.
Unrest has erupted over the past week - largely in loyalist, Protestant areas - amid rising tensions over post-Brexit trade rules and worsening relations between the parties in the Protestant-Catholic power-sharing Belfast government.
UK Prime Minister Boris Johnson condemned the unrest, saying "the way to resolve differences is through dialogue, not violence or criminality".
He sent Northern Ireland Secretary Brandon Lewis to Belfast for talks with the region's political leaders.
Meanwhile, Northern Ireland's Belfast-based assembly and government held emergency meetings on Thursday and called for an end to the violence.
First Minister Arlene Foster, of the pro-British Democratic Unionist Party, warned that "Northern Ireland faces deep political challenges ahead".
"We should all know that when politics are perceived to fail, those who fill the vacuum cause despair," said Foster, who heads the Northern Ireland government.
Deputy First Minister Michelle O'Neill, of Irish nationalist party Sinn Fein, called the violence "utterly deplorable".
Despite the united message, Northern Ireland's politicians are deeply divided and events on the street are in many cases beyond their control.
The latest disturbances followed unrest over the Easter long weekend in pro-British unionist areas in and around Belfast and Londonderry, also known as Derry, in which cars were set on fire and projectiles and petrol bombs hurled at police officers.
Some politicians and police have accused outlawed paramilitary groups - which remain a force in working class communities - of inciting young people to cause mayhem.
They expressed outrage that a new generation was being exposed to and pulled into violence.
Australian Associated Press
