Police investigating house parties in South Belfast found a group of people hiding in a bathroom.
Some of those present early on Thursday received community resolution notices, while the behaviour of others resulted in fixed-penalty notices.
It follows a series of arrests for a range of coronavirus-related offences in the Holyland district near Queen’s University over recent days.
PSNI Chief Inspector Gavin Kirkpatrick said: “Some young people who have moved to the area to pursue their studies, and others visiting the area, are not listening to our repeated warnings.
“Alongside the universities and colleges, we have issued multiple appeals for young people to follow the latest health and safety advice and highlighted the importance of being good neighbours.
“Last night, we gave advice and guidance at a number of residential properties. However, 18 of those people we spoke with failed to understand the seriousness of the situation.”
Police issued 10 community resolution notices and eight fixed-penalty notices, which carry a £60 fine.
Police have dedicated “substantial resources” to policing this area throughout the coming weeks and say they will “robustly” address any anti-social behaviour and criminal offences.
University classes are due to resume in the coming weeks.
Mr Kirkpatrick said: “Where appropriate, we now will liaise with the universities and colleges who will consider their own sanctions against any students involved.
“Our message is very clear: all students must follow the health and safety advice and specific guidance regarding houses of multiple occupancy provided by the universities.
“Only six people, from a maximum of two different households, can gather indoors in a private dwelling.”