The Chief Medical Officer has expressed concern about Covid-19 outbreaks in workplaces and as a result of gatherings for Christmas parties and funerals.
Dr Tony Holohan urged people to heed the public health advice, including limiting their contacts, to avoid a big increase in cases next month.
"We are now getting reports of outbreaks in social settings including workplace settings, Christmas parties and funerals.
"I cannot stress enough how important it is to limit your interactions now. The consequences of not doing so will be exponential growth in January, a substantial increase in hospitalisations and risk to life," Dr Holohan added.
The Department of Health has been notified of 484 cases of Covid-19 today and three virus-related deaths.
The number of people in hospital is 200, with 31 of the patients in intensive care, up one from yesterday.
Nationally, the 14-day incidence rate of the virus per 100,000 of the population is 94.2.
'I cannot stress enough how important it is to limit your interactions now,' Dr Tony Holohan said
Dr Holohan said the five-day moving average is 387 per day and the virus is spreading throughout the country in all age groups.
Deputy Chief Medical Officer Dr Ronan Glynn urged people to limit their social contacts and "consider whether now is the time to be meeting with them".
Professor Philip Nolan, chair of NPHET's Irish Epidemiological Modelling Advisory Group, said the reproduction number of the virus is now estimated between 1.1 and 1.3.
Speaking at a National Public Health Emergency Team briefing this evening, Prof Nolan said: "We are concerned that Ireland is now in a phase of rapid growth, which if allowed continue, will result in 700- 1,200 cases per day by the second week in January, if not sooner.
"We are particularly concerned about older people and vulnerable adults, who have protected themselves through the second wave, and are now at risk during the festive season," he added.
Prof Nolan said that "whatever we were doing" between 1 and 7 December "was too much, too much social mixing and here we are now. We need to stop now to protect where we were going to be in seven to 10 days."
Daily virus count (bars) five-day average (line)
Dr Holohan said that many people's plans for Christmas are perfectly good and do not need to be changed. But he said that people need to look again at them to make sure they are safe.
He said there is a rising tide of infection across the country and no area is safe, adding that the basic message remains to wear masks, stay away from crowds and limit social contacts.
Dr Holohan said that people with symptoms should self-isolate and contact their GP for advice. He said they should not go out shopping or socialise.
He said it would be "a terrible tragedy for many people if they picked up an infection that is largely preventable through not following public health advice" when the possibility of getting a vaccine is close.
Model projections of the number of new cases per day
Dr Glynn said that people should keep gatherings as small as possible but it was not just about the size of them.
If people have any symptoms they should self-isolate and should not feel under pressure to attend family gatherings, he added.