Four police officers have been injured during rioting linked to union flag protests in Northern Ireland.

Police fired five plastic bullets as rioters threw more than 30 petrol bombs. The most serious violence took place in parts of County Antrim.

A crowd of over 100 loyalists threw missiles at police in Carrickfergus.

Fireworks, petrol bombs and rocks were used to attack police in the O'Neill's Road area of Newtownabbey. A bus was set alight near the Rathcoole estate.

This violence is unacceptable, these rioters are harming their own community. The scenes in Carrickfergus and Newtownabbey are a disgrace Stewart Dickson, Alliance MLA

Meanwhile, a viable pipe bomb was found after a security alert on the Westlink, Belfast's busiest road.

Loyalist street protests have being taking place for almost six weeks, since Belfast City Council voted to change its longstanding union flag policy on 3 December.

The council, which now has more nationalist members than unionists and with the Alliance party holding the balance of power, voted to fly the flag at Belfast City Hall on a number of designated days, rather than every day of the year.

The majority of the street demonstrations have passed without incident, but some have resulted in serious rioting.

Media playback is unsupported on your device Media caption Andy Martin: "Concrete blocks were being smashed up...some by children as young as eight"

Dozens of police officers have been injured in almost 40 days of protests and more than 100 people have been arrested.

On Friday night, two arrests were made. Of the four police officers who were injured, one required hospital treatment.

A PSNI spokesman said police "will continue to pursue a vigorous evidence gathering operation to bring those involved in the violence to justice".

Friday's protests - most of which passed without violence - took place in Counties Antrim, Armagh, Down, and Londonderry.

They began in some areas at 15:00 GMT, causing disruption to traffic and blocking and many arterial routes in Belfast.

Translink withdrew all its bus services in Belfast, apart from Falls Road services and buses to Belfast International Airport.

There have been no reports of violence in the city itself and all roads are now open again.

However, in County Antrim, police used water cannon during trouble on the Shore Road in Whiteabbey and also in Newtownabbey, where a PSNI Land Rover with a CCTV camera on the roof was set alight with a petrol bomb.

In Rathcoole in Newtownabbey, a distressed pensioner pleaded with protesters to let him pass through a road block so he could make his way to visit his seriously ill wife in hospital.

Media playback is unsupported on your device Media caption Listen as man argues with protesters

The protesters jeered at the elderly man and refused to let him through.

Stewart Dickson, an Alliance MLA for East Antrim, said the protests on Friday night had caused "widespread misery".

He said: "This violence is unacceptable, these rioters are harming their own community. The scenes in Carrickfergus and Newtownabbey are a disgrace.

"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."

Last month, Mr Dickson's Alliance party office in Carrickfergus was severely damaged in an arson attack - one of several attacks on the homes and offices of political representatives since the protests began.

In Belfast, thousands of Ulster rugby supporters encountered delays getting to Ravenhill stadium in the east of the city for Friday night's Heineken Cup pool match between Ulster and Glasgow.

There were also protests in Glasgow and in Liverpool at 18:00 GMT on Friday.

Operation Sit In

Meanwhile, people used social media to initiate Operation Sit In - a counter to the protests that encouraged people to come out regardless and support their local pubs or restaurants.

Stephen Magorrian, the managing director of Botanic Inns, said people could have a great night out in the city centre.

"There is great entertainment, so stay in the city. We need the support.

"Things are still going and we have some of the best restaurants and bars, but if we don't support them we will lose them."