Two people have been arrested following minor trouble in Londonderry before the annual Apprentice Boys parade.
An articulated lorry was hijacked by a number of men and set alight in the Bogside and four cars were burnt out during sporadic violence just hours before the march.
The trouble has not affected the event and the police have described the incidents as minor.
A number of small feeder parades have passed off without incident.
The governor of the Apprentice Boys, William Allen, said he was disappointed.
"There will always be trouble, it does not matter how many parades you have there will always be someone who will come along to cause disruption," he said.
"It is something you accept.
"You don't like it, you don't want it but there is nothing you can do about it really."
Saturday's march is the largest Loyal Order demonstration in Northern Ireland, with the main parade getting underway about lunchtime.
After a small parade in the loyalist Fountain estate, local Apprentice Boys completed a walk of Derry's historic walls.
The wreath laying ceremony at the war memorial in the Diamond was followed by a religious service in St Columb's Cathedral.
The Siege of Derry in 1688 was re-enacted before marchers began the main parade.
As the marchers were passing through the Diamond area, a banner was unfurled at the top of the Richmond shopping centre in support of republican prisoners - demanding segregation at Maghaberry jail in County Antrim.
Superintendent Johnny McCarroll said the disturbances had not affected the parade itself.
"I have no doubt that it has been organised to try to disrupt the parade," he said.
"But that has not happened, the parade has gone ahead and it has remained peaceful in the city centre.
"We hope that will continue throughout the day."
Meanwhile in Belfast, a number of "feeder" parades through nationalist areas passed off peacefully.
A small group of nationalist protesters congregated at Ardoyne shops in north
Belfast but there was no trouble.
Sinn Fein strongly criticised the Parades Commision's decision to allow the Apprentice Boys to march past the Ardoyne and Mountainview areas on Saturday.
The government established the Parades Commission in 1998 to make decisions on whether controversial parades should be restricted.
Commission rulings restricting marches by the Protestant loyal orders, which are opposed by nationalist residents, have led to calls by unionist politicians for the body to be scrapped.