Large demonstrations have been held since the City Council voted in early December to fly the Union Jack over City Hall only 17 days a year. Many turned into stone-throwing riots.
The flag had flown daily over City Hall since it was built more than a century ago. The City Council narrowly approved a compromise put forward by the Alliance Party, whose officials have since received death threats.
Thursday's protest was in a loyalist area in East Belfast on the border of the Catholic and nationalist Short Strand neighborhood, The Guardian reported. About 100 people gathered, throwing Molotov cocktails at the police and setting cars on fire.
Another demonstration was planned for Friday with protesters saying they would set up road blocks.