There's an "immediate need" for care and caution, as the COVID-19 reproductive rate now stands "at or above one".
That's according to the National Public Health Emergency Team (NPHET), as today's figures show a further six people with the virus have died.
23 new cases have also been confirmed, with all of today's new cases involving people under the age of 45.
The 'R number' shows the average amount of people that an infected person will pass the infection on to.
Chair of the COVID Modelling Advisory Group, Professor Philip Nolan said it's concerning news.
He said: "It looks like each case currently is leading to another case. We'd prefer it wasn't, and [are] working hard to ensure it doesn't.
"I think the note of caution is that we have clusters and outbreaks, and each and every one of us needs to do everything we can to ensure a cluster or outbreak doesn't lead to unnecessary further transmission of disease.
"[It's] a note of caution... not yet a note of alarm."
Officials also say there's a "clear change" in the way COVID-19 is spreading, with younger people now accounting for the vast majority of cases in this country.
All of the 23 newly-confirmed cases are people under 45 years of age, with 15 under the age of 25.
