Belfast , Northern Ireland ( CNN ) -- Fresh pro-British protests erupted Saturday in the Northern Ireland city of Belfast , police said , hours after nine officers were hurt in rioting . Tensions have been high since city council members there voted a month ago to stop flying the Union flag year-round , restricting it instead to certain days . Officers came under sustained attack in east Belfast from more than 100 people , some throwing fireworks and bricks , the Police Service of Northern Ireland said Saturday . The violence continued into the night . Police said they deployed water cannon and fired plastic bullets and that a number of arrests were made . Authorities were also investigating reports that a number of shots were fired at police lines . Friday night , more than 30 petrol bombs were thrown at officers during serious disorder in the same part of the city . Officers were also pelted with ball bearings , fireworks and masonry , police said . Eight officers were hurt . Another officer was hurt Friday in the Newtownabbey area , police said , where bottles and bricks were thrown at police in the course of a protest lasting several hours . Police have arrested more than 20 people in connection with the disorder . A lunchtime demonstration outside City Hall appeared to pass without trouble . Northern Ireland 's political leaders have called for an end to the pro-British protests , which were prompted by the vote on the Union flag of the United Kingdom . The disorder follows a summer of heightened tensions between Northern Ireland 's Catholic and Protestant communities . Riots in September left dozens of police officers hurt . The recent violence follows more than a decade during which Northern Ireland has made steady progress toward lasting peace and stability . More : Policewoman targeted as tensions rise . More : Police -- Loyalist paramilitaries behind violence .
Further violent pro - British protests broke out in Belfast , police say . Nine police officers were injured Friday . They pelted officers with petrol bombs , fireworks and bricks , police say . Protests have affected parts of Northern Ireland since a vote on the Union Bill .