However, its implementation has to date proved contentious and problematic, with the new regulatory and customs processes now required to bring goods into Northern Ireland from the rest of the United Kingdom, triggering lengthy delays at the province's ports, while also sparking growing unrest among unionists and loyalists at the presence of an Irish Sea trading border.

UK Prime Minister Boris Johnson on Wednesday (7 April) said he was deeply concerned by scenes of violence in Northern Ireland after crowds of youths in a pro-British area of Belfast set a hijacked bus on fire and attacked police with stones.

He added: "The way to resolve differences is through dialogue, not violence or criminality".

People also lobbed bricks, fireworks and gasoline bombs Wednesday night in both directions over a concrete "peace wall" that separates Protestant, British loyalist, and Catholic, Irish nationalist neighbourhoods. Police fired rubber bullets at the crowd, and nearby a city bus was hijacked and set on fire.

During several hours of disorder police officers were attacked, petrol bombs were thrown and a bus was burnt.

In a statement, Irish Taoiseach Micheal Martin condemned the violence and "attacks on police", adding the "only way forward is to address issues of concern through peaceful and democratic means".

My Government has listened to and will continue to listen to and engage with the views of all communities in Northern Ireland.

Sinn Fein and others have accused the Democratic Unionist Party (DUP) of First Minister Arlene Foster of stoking tensions with their staunch opposition to the new trading barriers that many unionists feel erases part of their identity.

Peel Region schools move classes online
Lawrence Loh, Peel's medical officer of health, who will be exercising his discretionary powers to enact such closures under Sec. Next week is spring break for most elementary and secondary students across the province.

"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.

The British-run region's devolved executive, a compulsory power-sharing coalition led by Irish nationalists and their unionist rivals, will meet later on Thursday to discuss the clashes, Deputy First Minister Michelle O'Neill said.

The unrest on Wednesday evening was the most serious Northern Ireland has seen in years, Mr Roberts said.

A post-Brexit U.K. -EU trade deal has imposed customs and border checks on some goods moving between Northern Ireland and the rest of the U.K. The arrangement was created to avoid checks between Northern Ireland and Ireland because an open Irish border has helped underpin the peace process built on the Good Friday accord.

While politicians from all sides condemned the clashes on Wednesday, Northern Ireland's main governing parties blamed one other.

Katy Hayward, a politics professor at Queen's University Belfast and senior fellow of the U.K.in a Changing Europe think tank, said unionists felt that "Northern Ireland's place is under threat in the union, and they feel betrayed by London".

The violence has been blamed on anger in response to a decision by the Public Prosecution Service not to pursue prosecutions against members of Sinn Fein who attended the funeral of Mr Storey previous year despite restrictions over gatherings, as well as Brexit and localised issues in the south-east Antrim area.

There are also tensions over the police's handling of alleged lockdown breaches by Sinn Fein at the funeral of republican Bobby Storey. "There's many factors, including, obviously, criminal gangs at work who benefit from chaos like this".