Police are dealing with low-level disorder in Belfast's Holyland.
The area is busy with St Patrick's Day revellers. Officers have a mobile cell van in case of trouble.
Superintendent Robert Murdie said: "We are experiencing some low-level disorder, some on-street drinking.
"So we are now working with our partnership agencies to try to address this situation and would make an appeal, certainly to young people, not to come into the Holyland area and also to parents, know where your young people are."
Five people were arrested on Thursday night for minor drink-related offences in the area, police said.
There has been a heavy PSNI presence. Senior officers said the conduct of most people was very positive.
Five local off-licences closed voluntarily for some time on St Patrick's Day.
Street disturbances and anti-social behaviour have bedevilled the area at this time of year in the past.
The district behind Queen's University is full of student housing.
Queen's and Ulster University have said the majority of those who travelled there on previous St Patrick's Days were post-primary pupils or non-students.
Revellers who engage in anti-social behaviour may be dismissed from their studies, Ulster University has warned.
Vice-chancellor Paddy Nixon said he was extremely concerned about behaviour by a minority of students in the Holyland area.
Several Ulster University students have been disciplined for engaging in anti-social behaviour in recent years.
Meanwhile, St Patrick's Day parades were held in Belfast, Londonderry, Downpatrick, Armagh and Newry.
A carnival march left Belfast's city hall at midday.
A free concert with X Factor runner-up Fleur East, Reggie 'n' Bollie and Stooshe was held at Custom House Square.
Traditional music and "make your own shamrock" workshops also entertained crowds at St George's Market.