Business owners need to be prepared for the possibility that they may not reopen until the end of March, Tánaiste Leo Varadkar has warned.
It came as the Government announced tough new restrictions aimed at stemming the massive surge in Covid-19 cases.
Taoiseach Micheál Martin urged people to face the coming weeks with "steely determination and resolve". He said personal decisions people make will "directly affect how many more people get sick and how many more people die".
Measures in place until at least January 31 include:
:: Schools staying closed to all but Leaving Cert and special needs students;
:: Childcare services like créches will be for essential workers only;
:: Work will halt on most construction sites apart from certain projects like hospitals and some social housing;
:: People travelling from Britain will have to produce a negative Covid-19 test.
Mr Martin, meanwhile, said people should "forget about take-away pints" and publicans should not be selling them as they can lead to gatherings that spread the virus.
Garda checkpoints will be returning today as part of additional policing measures due to Level 5 lockdown.
Static checkpoint under Operation Fanacht will recommence from 7am on national roads - not motorways - with random local mobile checkpoints designed to support the "stay home" message.
The Courts Service announced no new Central or Criminal Court trials would begin this month. Some longer trials involving larger numbers of defendants and witnesses had been due to begin at Croke Park but these will not start until February at the earliest.
Announcing the new restrictions, Mr Martin said: "We are in a battle against the deadly and ever changing virus.
"The lockdown we're introducing today is designed to reflect that stark and simple reality. Unless you're involved in absolutely essential work you have no reason to be away from your home."
Mr Varadkar said there is hope in the form of Covid-19 vaccines but the vulnerable must be protected until they can be inoculated.
"January is the month in which we all stay in," he said.
Mr Varadkar set out a timeline that would see nursing home residents, healthcare staff, very elderly people and those with chronic illness vaccinated by the end of March.
The hospitality sector has been closed since Christmas Eve and the Enterprise Minister was asked if pubs and restaurants may need to stay closed until then.
Mr Varadkar said the timeline he described is with use of the Pfizer/BioNTech and Moderna vaccines and it could be stepped up more if the Astrazeneca one becomes available. But he added: "If I was running a business now I would be thinking that it's a probability that I'll be closed until the end of March."
He added: "In case I put the heart across people we will review the situation on January 30 and make decisions on restrictions then."
"The situation is deteriorating. It is very bad. It is going to get worse in our hospitals and ICUs. We're not going to be out of the woods by the end of January".
Supports like the Pandemic Unemployment Payment (PUP) and weekly payments for businesses which are closed will continue until at least March 31 "in case things go on that long". He added: "I think anybody in the business community needs to be prepared for that possibility." Up to 500,000 people may end up on the PUP.
Mr Varadkar said the Government is engaging with banks to ensure they provide additional payment breaks to mortgage holders and people with loans who can't meet the payments as a result of the crisis and the response so far has been "positive".
Both Mr Martin and Education Minister Norma Foley spoke of how it's still the Government's intention to hold the traditional Leaving Cert exams this summer and said the public health advice is that schools are a safe environment.
Leaving Cert students will be able to attend their schools for three days a week under the Government's plan.
Mr Martin said the move would mean there would be around 61,000 people travelling to and from schools rather than more than 1m students and teachers if they were left fully open.
Asked about the possibility of a rebate scheme for parents paying fees for creches whose services they can't use, Mr Martin said Children Minister Roderic O'Gorman is examining the matter.
A Department of Children statement said Mr O'Gorman is asking that providers pause payment of fees or return fees paid in advance for parents who are not essential workers.
The resumption of the ECCE pre-school programme has been postponed until February 1 with other services open for the children of essential workers only.
A household of an essential worker, without an existing childcare arrangement, can form a bubble with another household so their child can be looked after.
Transport Minister Eamon Ryan said the ban on travel from Britain, which has been at the centre of an outbreak of a highly transmissible new strain of the virus, will be lifted on Saturday.
Passengers coming from the UK by air or sea will be required to produce a negative PCR test result they got within 72 hours of travel. Failure to do so could result in a €2,500 fine or up to six months in prison.
Mr Ryan said requirement for the test will be extended to other "red list" countries in the coming weeks.