The PSNI says two police officers were injured during a disturbance in Belfast city centre last night.
Two people were arrested for public order offences.
The trouble broke out in Castle Street as the officers tried to make the first arrest.
They were surrounded by a hostile crowd and a short time later came under attack at nearby Castle Junction, when bottles and other missiles were thrown.
The trouble happened as people were leaving the annual switching on of the Christmas lights in the city.
Belfast's Lord Mayor, Councillor Jim Rodgers, said he was angry and disappointed at what had happened.
He condemned what he called 'the drunken thugs' involved, saying it was 'rather sad' that some people suffered and had to run to get away from the incident.
Meanwhile in North Belfast, four teenagers were arrested for public order offences after police were called to a disturbance involving a large group of people at Carlisle Circus.
The PSNI spokesman said the youths were aged 15, 17, 18 and 19.