( CNN ) -- Police in Northern Ireland appealed for the community 's help after a fourth night of Catholic-Protestant violence in Belfast , which saw a number of officers injured . Five people , all in their teens or early 20s , were arrested in connection with the unrest , police said . Wednesday night 's violence began shortly before 8 p.m. ( 3 p.m . ET ) and lasted for about six hours , the Police Service of Northern Ireland ( PSNI ) said . Are you there ? Share your stories , photos and videos . In one incident , a car was stolen as the driver was getting inside and the vehicle was then set on fire , police said . Assistant Chief Constable Duncan McCausland said Wednesday 's violence involved a smaller group of people than on previous nights and included a `` hardcore group '' of about 12 people . Northern Ireland 's marching season begins . They threw objects including petrol bombs and fireworks at police . Police fired back with stun grenades and water cannons , they said . `` A number '' of police officers were hurt but their injuries were not believed to be serious , the PSNI said . The violence began over the weekend after a decision to allow a Protestant parade to pass through a mainly Catholic neighborhood on July 12 , a day when Protestants march to celebrate the victory of England 's King William III over his ousted Catholic predecessor , James II , in 1689 . Known as The Twelfth , the holiday has previously been marred by violence and has been a source of tension between Catholics and Protestants for years . Police had to remove demonstrators who staged a sit-down protest to block this year 's march . Rioting erupted a short time later and more than 50 officers were hurt . The previous night , 27 officers were hurt , including three who were shot at close range by a masked man armed with a shotgun . McCausland said community leaders helped with the situation Wednesday night , but he urged them to do even more . `` A number of community workers worked hard to exercise their influence last night and I would thank them for that , '' McCausland said . `` However , I would ask them to redouble their efforts . In this way , working together , we can help bring these incidents to an end . '' British Prime Minister David Cameron on Wednesday denounced the `` completely unacceptable behavior '' of those involved in the unrest . He dismissed any sectarian cause behind the violence , pointing out Northern Ireland 's police force is under local control , no longer governed by London . `` There is no excuse for anyone not to cooperate with that police force , '' Cameron said .
Five people were arrested after a fourth night of violence in Belfast . Those arrested are all in their teens or early 20s . The police have said they will be seeking the arrest of any other suspects who may still remain at large, and that anyone with information should contact them on 0800 555 111. Police are appealing for more community help to deal with the unrest .