The chief medical officer has urged people to stick with social distancing for six months "like their lives depend on it".
Another 220 cases of Covid-19 were confirmed in the last 24-hour reporting period as the rate of infection surges.
Senior medic Dr Michael McBride said: "I ask you not to give up."
People are not allowed to visit inside other homes as Stormont reintroduces some restrictions seen earlier in the pandemic.
Ministers could face 600 new infections a day within a month if they had not clamped down, modelling experts believe.
The next two weeks will be critical in deciding whether they need to go further, health chiefs say.
Economy Minister Diane Dodds has sounded a warning that a fresh lockdown would destroy many struggling firms.
Dr McBride said the course of the virus was in people's hands and how they acted as this winter approaches.
"Your life, and potentially the lives of others close to you, does depend on it," he added.
The number of diagnoses is predicted to double every 10 days in a major onslaught on the health service if nothing is done, chief scientific adviser Professor Ian Young said.
New restrictions will limit hospital visitors to one once a week with certain exceptions.
It follows measures aimed at reducing mixing in private homes which experts blame for much of the rise in community transmission.
Health Minister Robin Swann said: "I do not want another lockdown, at the same time we have to keep all options on the table.
"The best way to avoid further restrictions on our lives is to follow the ones we have in place now."
Dr McBride said the number of hospital admissions was increasing by 50% a week.
Dr Paul Johnston, an intensive care doctor at Antrim Area Hospital, said some medical staff in areas like intensive care had sought psychological support for the episodes they have witnessed while caring for patients.
He said: "Prevention seems better than a cure that does not currently exist."
Read more:220 people test positive for Covid-19 in most recent 24-hour reporting period
Mrs Dodds said businesses were in a "perilous" state.
"The Northern Ireland economy cannot afford another lockdown. Those small shoots of recovery we are seeing would be destroyed."
Pubs welcomed back customers on Wednesday a day after additional restrictions limiting domestic gatherings were imposed across the country aimed at curbing spiralling infection rates.
Joanne Shilliday, owner of the Hole In The Wall pub in Armagh city, said: "We'll get through it, we'll do whatever we have to do, whatever regulations are in, we'll do what we have to to stay open.
"The Guinness seems to be going down well so far."
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.
Holy Cross College in Strabane, Co Tyrone, announced it was shutting its gates on Wednesday morning after recording confirmed infections.
Two were confirmed on Sunday September 20 and two more today. A deep clean of the secondary school for around 1,550 boys and girls was undertaken.
Malone Integrated College in Belfast reported a positive case among the teaching staff.
Meanwhile, in the Republic of Ireland another 234 new cases of Covid-19 have been diagnosed, the National Public Health Emergency Team has said.
There have been two further deaths linked to the pandemic.
