Eighteen police officers have been injured during serious rioting in the centre of Omagh, Co Tyrone.
The PSNI said up to 200 people were involved in the violence early yesterday during which paving stones were ripped up and a wall knocked down to provide ammunition to hurl at officers.
What appeared to start as a drunken brawl outside a nightclub on Castle Street at 2 a.m. developed into more extensive violence lasting two hours.
Fifteen people, including juveniles, were arrested for public order offences.
Insp Paul Douglas of the PSNI described the trouble as "mindless violence".
Closed circuit TV cameras in the area were attacked and one damaged during the rampage.
Insp Douglas said an extensive inquiry had been mounted and all evidence would examined including footage from the CCTV cameras.
Local SDLP councillor Mr Pat McDonald said what began as drunken brawling quickly developed into more serious trouble.
"Assaults took place and attacks took place on the security cameras which operate in that part of the town," he said.
"This led to police intervention and pretty serious rioting with bottles and stones being thrown at police."
In Derry, meanwhile, a man was. seriously injured in a gun attack on a house.
Police said he suffered cuts to the face when a shotgun blast was fired into the living room of the house at Milltown Crescent in the Waterside district.
Six other people, including a nine-year-old girl, escaped injury but suffered shock.
Police said there was no obvious motive for the attack.
In north Belfast, petrol bombs were thrown during the night during a brief confrontation between nationalist and loyalist youths.
A pregnant woman was taken to hospital after the trouble on the Limestone Road.
Sinn Féin said nationalists had been braced for loyalist attack following the ending of the loyalist feud.
Meanwhile a young man was recovering in hospital after being shot four times in north Belfast.
He was shot in both arms and legs at Carlisle Walk in the New Lodge area. Paramedics treated him at the scene before he was taken to hospital.
In Lisburn, Co Antrim, a man was seriously injured when he was assaulted by masked men wielding baseball bats.
They attacked him as he walked along the street and inflicted severe cuts and bruises requiring detention in hospital. - (PA)