Up to 600 people a day could be told they have contracted Covid-19 in Northern Ireland if the brakes are not applied to its spread.
The warning from the chief scientific adviser comes six months to the day the UK went into lockdown - and as one school in Co Tyrone closed suddenly this morning, leaving 1,600 pupils to return home.
Northern Ireland's infection number is predicted to double every 10 days adding immense pressure to the health service.
Professor Ian Young said a "circuit breaker" lockdown of up to three weeks may interrupt the virus's spread but says it is not likely to happen soon.
He told the Nolan Show: "We are sitting at 150 cases a day at the moment. In four weeks I would expect us to be, if nothing was done, I would expect us to be at at least 500 to 600 cases a day.
"Even one death is a death too many and we know that there would certainly be deaths," he added.
Pubs that do not serve food are due to open in Northern Ireland on today, despite fresh Covid-19 restrictions.
It comes a day after additional restrictions limiting domestic gatherings were imposed aimed at curbing spiralling infection rates.
Restrictions on households were extended across the country on Tuesday evening.
There can be no mixing of households indoors, with some exemptions, while no more than six people from two households can meet in a garden.
Previously, the measures only applied to Belfast and Ballymena in Co Antrim.
Reopening of wet pubs happens today after being closed from March 23. Those serving food were allowed to open in July.
Northern Ireland's leaders acknowledged on Tuesday that Stormont's latest Covid-19 messaging had become confused.
First Minister Arlene Foster said the measures must act as a wake-up call.
