Fresh rioting erupted last night with violent clashes between nationalist youths and police at the traditional flashpoint area of Ardoyne in north Belfast.
Police fired plastic bullet rounds and deployed water cannon against rioters who pelted them with petrol bombs, bricks, bottles, fireworks and stones. A number of officers were injured.
Minor disturbances also took place in a number of other locations, both loyalist and republican, with vehicles hijacked and set on fire. In Londonderry a 14-year-old was arrested on suspicion of rioting.
The Ardoyne trouble broke out after an Orange march passed close to the Catholic area, where republican dissidents were determined to register their opposition.
On previous nights 22 police officers were injured as both loyalist and republican mobs used petrol-bombs and other missiles against them, though none of them was seriously hurt.
Police were stretched by the fact that disorder broke out in more than half a dozen separate locations in and around Belfast. Sixty new armoured Land Rovers were instantly brought into service, plastic bullets were fired and water cannon deployed.
In recent weeks rioters have driven hijacked vehicles, sometimes on fire, towards police lines.
Few arrests have been made, since the police approach is usually to hold rioters at bay. Instead of using "snatch-squad" tactics, which carry the risk of inflaming trouble, police generally prefer to bring charges at a later date, often relying on closed-circuit TV evidence.
In recent times rioters have however increasingly worn woollen balaclavas to avoid identification. Dissident republican groups who indulge in full-scale terrorism send their members to flashpoints where they encourage local youths, who are often involved in petty crime, to take on the police.
Sinn Fein in west Belfast said yesterday that a local riot had been caused by "anti-social elements" coming together at one spot, saying: "There was clearly no rationale for gathering other than the purpose of having a riot.
"People came from other parts of Belfast, who would be known as anti-social elements, who had taken a lot of drink and were attacking the police.
"Those behind it are not welcome here. When it is all done the local community are left to pick up the pieces."
On the loyalist side rioting which took place in a number of normally peaceful locations north of Belfast was sparked when police moved in to remove a number of paramilitary flags.
While the police bore the brunt of the widespread violence other emergency services also came under attack. In west Belfast the windscreen of a fire engine was smashed by youths throwing bricks and bottles, while an ambulance crew was attacked after responding to a hoax call.
A fire service spokesman said: "We had over 200 incidents last night. It was very busy and challenging – we were dealing with a call every 75 seconds at one stage."