A number of cars and a bus were set on fire in County Down during disorder on the Eleventh Night.
It came after the PSNI warned that the East Belfast UVF "intend to orchestrate serious disorder" against police officers.
Eleventh night bonfires took place across Northern Ireland.
A "number of cars were on fire" in Dundonald while a bus was burnt out in Newtownards, police said.
Other flashpoints on Wednesday night included:
- An incident on the Sydenham bypass that kept passengers temporarily inside Belfast City Airport
- Petrol bombs and missiles thrown in the Bogside and Galliagh areas of Londonderry
- Almost 200 emergency calls received by the NI Fire and Rescue Service, with 95 "operational incidents" of which 13 were bonfire related
- Firefighters coming under attack in the Carnhill area of Derry, leading to slight damage to a fire engine
'UVF to orchestrate disorder'
Bonfires are traditionally lit in many loyalist areas of Northern Ireland on the Eleventh Night - the eve of the Twelfth of July.
The Northern Ireland Fire and Rescue Service said it had received 198 emergency calls between 18:00 and 23:00.
It said there were "95 operational incidents" of which 13 were bonfire related.
It also said a fire engine was "slightly damaged" when crews were attacked in the Carnhill area of Derry but that "no personnel were injured".
Earlier on Wednesday, the police issued a statement warning they had information that "the East Belfast UVF intend to orchestrate and participate in serious disorder in east Belfast this evening" against police officers.
"I would strongly urge people to desist from engaging in any violent or criminal behaviour," said Assistant Chief Constable Alan Todd
"I would also appeal to those who have influence in this community to discourage people from taking part in any illegal activity."
In Dundonald, the PSNI said officers were on the scene on the Upper Newtownards Road following reports of a number of cars on fire.
It said it was reported that "a number of masked males pushed a car into the road and set it on fire close to Robbs Road" at about 21:45.
There was a further report that two cars were set on fire close to Carrowreagh Road.
"We would like to the thank the members of the public who are currently assisting us as we try to identify these individuals who appear determined to obstruct the road network, particularly so close to the Ulster Hospital's accident and emergency department," the police said.
In Newtownards, police said was a bus was hijacked at about 19:30 on Wednesday in Blenheim Drive.
They said the hijack was carried out by a gang of masked men, one carrying a suspected firearm, before it was set on fire.
A number of passengers who were in the bus at the time were not injured.
The police said that the bus has been removed and Blenheim Drive reopened.
At Belfast City Airport passengers were kept inside while police dealt with an incident on the Sydenham Bypass.
Police had temporarily closed the road in both directions as officers searched the undergrowth in nearby streets.
Trains did not call at Titanic Quarter due to the security alert.
The Sydenham bypass reopened at about 21.30 and the airport returned to operating normally.
Earlier on Wednesday, material was removed from two bonfire sites in east Belfast.
Concerns had been raised over the safety of the Cluan Place and Bloomfield bonfires.
On Tuesday afternoon, a device believed to be a pipe bomb exploded in the nationalist Short Strand area, near to Cluan Place.
Pallets lit in Bogside
In Derry, the PSNI closed the city's walls earlier on Wednesday after they came under attack.
A strong police presence, including officers in full riot gear, has been on stand-by in the area between the Bogside and the predominantly Protestant Fountain estate.
A number of pallets were also lit on a road in the Bogside earlier on Wednesday night.
It followed several nights of disorder in the Bogside area, as well as attacks on the Fountain estate.