Apprentice Boys parade under way
Northern Ireland's Justice Minister David Ford has appealed for calm ahead of the Apprentice Boys Relief of Derry parade in Londonderry later.
A large-scale security operation in the city centre was launched ahead of the main parade at 1230 BST.
Up to 15,000 people and 140 bands are expected to attend.
Meanwhile, a protest at the north Belfast feeder parade before the Apprentice Boys travel to Londonderry has passed off without incident.
More than 50 nationalists protested at the Ardyone shopfronts early on Saturday morning as the Apprentice Boys marched past.
The first part of the Derry parade also took place earlier, with Apprentice Boys accompanied by nine bands completing a circuit of the city's historic walls.
A wreath-laying ceremony at the Cenotaph and a religious ceremony at St Columb's Cathedral took place before the main parade started.
Ahead of that, Mr Ford said no-one wanted a repeat of the violence which had affected Northern Ireland over the Twelfth of July period.
"The people of Northern Ireland have made it abundantly clear that they do not want violence on our streets," he said.
"I want to take this opportunity to appeal to anyone who might think that violence this weekend will achieve anything to step back and think again.
"Violence is not the way forward.
"It only serves to damage the daily lives of ordinary people - people who have shown time and again that they want a peaceful future where differences are resolved through dialogue."
Ch Supt Stephen Martin, from the Police Service of Northern Ireland, said: "My message to any troublemakers is stay away, because if you create trouble we will arrest you.
"If we don't arrest you at the time we will arrest you shortly afterwards and we'll put you before the court."
There were three nights of rioting by republicans in Ardoyne in north Belfast starting on 12 July, when an Orange Order parade passed in the area.
The Parades Commission has ruled that no band should accompany the Apprentice Boys Ligoniel Walker Club feeder parade as it passes Ardoyne shops on Saturday.
Meanwhile, a protest due to be held by dissident republicans in the centre of Londonderry on Saturday has been cancelled.
It was organised to highlight a dispute between dissident republican prisoners in Maghaberry jail and prison authorities.
However, following the intervention of mediators, the dispute was resolved on Thursday.
The protest on Saturday was due to coincide with the annual Apprentice Boys march.
Thirteen young Apprentices closed the gates of the walled city to stop the advancing forces of the Catholic King James' army in 1688.
Saturday's parade marks the relief of the city and the lifting of the 105-day siege in 1689.