Northern Ireland police said Sunday that Unionist protesters threw 30 petrol bombs at officers and torched cars during a night of "disorder" in a suburb of northern Belfast.

The violent clashes on Saturday evening came after protesters hurled manhole covers, masonry and petrol bombs at police late Friday in another loyalist neighbourhood and Northern Ireland Secretary Brandon Lewis appealed for calm.

North Area Commander Chief Superintendent Davy Beck in a statement released Sunday said some 30 protesters, some in masks, had gathered on Saturday evening.

Several dozen men mounted an "orchestrated attack on police", he said. A 47-year-old man was arrested and remains in custody.

There is rising discontent among unionist pro-British factions in Northern Ireland over arrangements linked to Britain's exit from the European Union.

The arrangements are aimed at preserving a fragile peace in the territory by preventing a hard border with EU member Ireland.

The protocol removes the need for customs and regulations checks on the border with Ireland by shifting checkpoints for goods arriving from mainland Britain to Northern Irish ports.

Unionists argue however that it strains ties with the rest of the UK by introducing trade barriers.

Tension has also been stoked this week by a decision not to prosecute 24 Sinn Fein party members who attended the funeral in June of Irish Republican Army figure Bobby Storey in blatant violation of COVID-19 guidelines.