Ireland could be facing 1,800-2,500 cases per day and more than 400 people in hospital by Halloween, according to the National Public Health Emergency Team (Nphet).
The virus is "uncontrolled" across the State, according to Dr Philip Nolan, as a further 1,205 cases were announced along with three further deaths.
Border counties which have moved into level four since midnight continue to show concerning rates of virus spread.
Cavan has the highest 14-day incidence rate per 100,000 at 639.3, almost double the next ranked county, Donegal on 367.5. Dublin's incidence rate is 206.7.
New: Three more Covid19 deaths. 1,205 new cases #iestaff— aoife moore. (@aoifegracemoore) October 15, 2020
"The case numbers are growing exponentially across the country, and we're concerned that growth is actually accelerating," said Dr Nolan, chair of the Epidemiological Modelling Advisory Group.
"The growth rate is 5% to 6% per day. The estimation was 4%-5% per day, with exponential growth and small changes, in 12 to 14 days, for the country as a whole, we estimate reproduction and hospitalisations increasing exponentially.
"The fact is that is increasing exponentially faster than we projected about 14 days ago.
For every 1,000 cases, that translates into hospitalisations, it certainly causes me concern about what that might look like in a (health) service, operating non-Covid services as well as exponential growth in Covid cases.
"It is inevitable that the disease will seep into vulnerable settings; that's not defeatist, that's what we're seeing.
"This is a message of seriousness and concern, but not hopelessness; more basic things can turn this around," said Dr Nolan.
In the Nphet statement announcing the Covid-19 figures, Dr Nolan said: "Modelling shows that if current trends continue, by October 31, the number of cases notified daily would be in the range of 1,800-2,500 cases with over 400 people in hospital."
Increasing concern has been flagged in people aged 18-24, where the incidence rate is three times higher than the next age bracket.
Nphet members said they were incredibly concerned about the trajectory amid data that shows people's behaviour has not changed.
There has been little decrease in the use of public transport or traffic indicators, and retail sales and debit card usage remains steady since the country moved into level three last week.
Dr Tony Holohan, the chief medical officer, said: "We're seeing too much of the kind of behaviour that ultimately facilitates the spread of the virus.
Dublin has been in level three for a week longer than the rest of the country, and although cases appeared to stabilise in the capital and a reduction of contacts, however, numbers are continuing to grow, though slightly slower than other counties.
In regards to the recent spate of anti-mask marches in Dublin and a full-page advertisement inthat criticised lockdown measures.
Dr Holohan said the topic had "become a debate but the science is abundantly clear. The HSE is working on public health messaging but we need all the help we can get, including from media, to get the message out in a clear and concise way."
Dr Ronan Glynn, the deputy chief medical officer, added that Nphet has heard "numerous stories" about people phoning their GP from work complaining of symptoms and asking for a test.
"The appeal to employers is to facilitate working from home and employees need to know it's not acceptable to come to work with flu symptoms or a new cough, the knock-on effects are profound."