Image caption A Translink bus was burnt out in the West Wind estate in Newtownards, County Down

Firefighters have been attacked, petrol bombs thrown and cars set alight during disturbances across Northern Ireland.

Most of the trouble was centred on Londonderry, east Belfast and parts of County Down as traditional Eleventh Night bonfires were lit in loyalist areas.

The fire service said there was a 23% increase in bonfire related incidents compared to last year.

Many bonfires passed off without incident.

Bonfires are traditionally lit in many loyalist areas of Northern Ireland on the Eleventh Night, the eve of the anniversary of the 1690 Battle of the Boyne, when William III - the Dutch-born Protestant better known as William of Orange or King Billy - defeated the Catholic King James II in County Meath.

Part of the Lower Newtownards Road was closed in the early hours of Thursday while police examined a hijacked car, but the road has now reopened.

Image copyright PAcemaker Image caption Part of the Newtownards Road was closed while a hijacked car was investigated

Police have confirmed that two "crude but viable" devices were left on the city walls in Derry at about 3.40am on Thursday.

DUP MLA for Foyle Gary Middleton said this caused "great concern".

"Effectively it is near the parade route as well, but we have the understanding from the PSNI that this will not in anyway affect the parade," he added.

"But at the same time these incidents need to be condemned because people don't want this activity on our streets."

Elsewhere, a number of cars were set on fire in Dundonald while a bus was burnt out in Newtownards, police said.

It came after police issued a statement warning on Wednesday that they had information "the east Belfast UVF intend to orchestrate and participate in serious disorder in east Belfast this evening" against police officers.

Masked men

Police said there were reports of a number of cars on fire on the Upper Newtownards Road.

The PSNI 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.

Image copyright PAcemaker Image caption Bonfires were lit across Northern Ireland

In Newtownards, police said a bus was hijacked at about 19:30 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 the bus has been removed and Blenheim Drive reopened.

Other flashpoints included:

An incident on the Sydenham bypass that kept passengers temporarily inside Belfast City Airport

Petrol bombs and missiles thrown in the predominantly nationalist Bogside and Galliagh areas of Derry

More than 320 emergency calls received by the NI Fire and Rescue Service, with 164 "operational incidents" of which 57 were bonfire related

Firefighters attacked in Derry, Moygashel and Ballycarry

Police condemned the disorder, which they blamed on a "small minority of people".

Assistant Chief Constable Alan Todd said: "No part of this is acceptable and today we are looking at the evidential picture to pursue lines of enquiry.

"I would like to pay tribute to the job that my officers, along with other emergency services, did last night."

Image caption One of the cars burnt out on the Eleventh night in Dundonald

A number of houses in the area have been evacuated.

Flags burned

In Derry there was a fifth consecutive night of violence, although it was reduced compared to the previous four nights.

Police closed the city walls to the public after petrol bombs were thrown from the Bogside.

Police said 16 petrol bombs in total were thrown at police in the vicinity of the city walls.

Some small fires also disrupted traffic on the nearby Lecky Road.

Petrol bombs also thrown at the police and a fire engine in the Collon Lane area of Carnhill.

In the Fountain estate, the national flags of Ireland and Palestine, as well as a Che Guevara flag were burned on a community bonfire when it was lit at midnight.

999 call every 48 seconds

The Northern Ireland Fire and Rescue Service said it had received 327 emergency calls between 18:00 and 01:00 and sent crews to 164 incidents, 57 of which were bonfire related.

It said between 22:00 and midnight there was a 999 call every 48 seconds.

"The most significant bonfire related incidents attended by NIFRS were in mid Ulster, Belfast, north Down and Causeway Coast and Glens," it said.

"Unfortunately during the evening there were three attacks on fire appliances in the Carnhill area of Londonderry, Moygashel [County Tyrone] and Ballycarry [County Antrim].

"Thankfully no firefighters were injured however damage was caused to an appliance."

Image copyright Declan McConaghy Image caption Passengers were kept inside Belfast City Airport as police dealt with an incident on the Sydenham bypass

At Belfast City Airport, passengers were kept inside while police dealt with an incident on the Sydenham Bypass in east Belfast.

Police temporarily closed the road in both directions as officers searched the undergrowth in nearby streets.

Image caption Police temporarily closed the Sydenham Bypass while they dealt with a security alert.

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.