A bus was hijacked and burned in Newtownabbey on Friday night as flag protesters forced the closure of roads across Northern Ireland.
There was also serious disorder in Carrickfergus where police used water cannon and fired five baton rounds during the disturbances.
Organisers of the demonstrations had called for a widespread show of support after mainly sporadic protests over the last six weeks.
Almost all passed off without incident but police were attacked with petrol bombs, fireworks and other missiles close to where the bus was burned near Rathfern in Newtownabbey.
The protests began on December 3 following a decision by Belfast City Council to restrict the flying of the Union Flag to designated days only.
There were simultaneous road blocks in the north, east and south of the city, as well as Bangor, Coleraine, Londonderry, Omagh, Enniskillen and several other major towns.
In Belfast, almost all Metro Bus services were cancelled for the evening.
The street demonstrations have continued despite recent political initiatives to calm tensions - including a DUP legal challenge to the flag’s removal from the city hall and the first meeting of the new Unionist Forum aimed at addressing loyalist grievances.
Four officers were injured – one requiring hospital treatment – and two people have been arrested. The PSNI said a total of 33 petrol bombs were thrown during the disturbances.
For over an hour there were simultaneous road blocks in the north, east and south of the city, as well as in Bangor, Newtownards, Coleraine, Londonderry, Omagh, Enniskillen and several other major towns.
There were also reports of flag protests in Glasgow and Liverpool.
In Belfast, all Metro bus services, with the exception of the Falls Road route, were temporarily suspended and some Ulsterbus services were also affected.
However, shortly after 8pm Translink announced that the suspended Metro bus services had been cancelled for the remainder of the evening.
South Belfast DUP councillor Ruth Patterson said she had attended protests in the Village, Taughmonagh and Finaghy areas and that all had passed off peacefully.
Speaking on Friday night, the former deputy mayor said: “I’ve been up to Taughmonagh and Finaghy and it’s all quiet. Great crowds at both protests but all very peaceful and dignified.”
Cllr Patterson described the burning of the bus in Newtownabbey was “probably the work of a wee hothead with nothing better to do”.
When asked if the apparent progress in the setting up of the Unionist Forum was likely to end the protests, she said: “This is very much a people event now. There is a sense of real anger on the ground in the community.
“People say it’s about the flag, deprivation and poor educational attainment, but every protest I have been to, the topic of conversation is the flag.
“Everything else will fall in behind that but the main topic of conversation is the flag having been removed from City Hall.”
Cllr Patterson said a lot of the protesters were people who would normally not be inclined to come on to the streets.
“The sense of anger, the sense of loss of identity and heritage - it has really hit hard and as I said before, I think it has shaken the Protestant/unionist/loyalist to the core, and that is why you have seen such a united front during the protests.”
With the 2012 ‘Our Time Our Place’ tourism initiative just ended, television footage around the world is showing images of public disorder.
Viewers as far away as Australia awoke on Saturday morning to news that: “Hundreds of pro-British youths blocked roads across Belfast on Friday evening and set a double-decker bus on fire in the latest protests against a decision to remove the British flag from Belfast City Hall.”
SDLP policing spokesperson Conall McDevitt has called for a “zero tolerance” approach from the PSNI in tackling the unlawful activity associated with some protests.
The South Belfast MLA said he recognised the right to peaceful protest but said many citizens would view further disruption as intimidating.
He added: “The right of protest does not, however, trump the other rights enshrined in the European Convention, particularly the rights to life, work, travel and a life lived free from intimidation. Protests which actively breach these rights, in part or in whole, are illegal and those who organise them are actively encouraging law-breaking.”
Alliance MLA Stewart Dickson said the demonstrations had caused widespread misery and a loss of earnings for traders.
Describing the violence as “a disgrace,” Mr Dickson said the rioters were only harming their own communities.
“This was just wanton violence. These protests have got nothing to do with a flag, it is about a major disconnect that has developed between protestors and those unionists that they have previously looked to for political representation.
“Despite the intimidation and lies told about the Alliance Party, we engage with everyone to move Northern Ireland beyond our bitter divisions into a genuine shared future.”
Full report in Saturday’s News Letter