As of midnight Thursday 17 September, the HPSC has been notified of 253 confirmed cases of COVID-19.
"Health services would be put at risk".
There are also 74 cases in hospital and 16 confirmed cases in ICU.
At a pressing briefing earlier this week, Mr Swann warned that the north was on a "knife edge".
However, 35-40pc of cases are linked with community transmission, meaning we don't know enough about how they got it to link these cases to a defined outbreak or other means of transmission.
Mr Swann said "intense" lockdown measures could be introduced if advised by public health officials. "Assume you and those you meet are infectious, keep your distance and do your part to keep others safe". It can work for us now.
"This is not a decision we have taken lightly but it is how we will suppress the virus".
Yesterday, the Health Protection Surveillance Centre reported 274 new coronavirus cases.
The total number of cases now stands at 8,943, including 763 in the last seven days.
The BT60 postcode, which covers sections of Co Armagh, on Friday evening became the latest area to face more curtailments, including discouraging indoor visits, with no more than six people from two households allowed to gather in a private garden.
To date, there have been 1,792 death associated with Covid-19. The death toll remains at 575. People working in Dublin are asked to work from home unless absolutely necessary.