The Irish government is now prioritising planning for a no-deal Brexit, according to its published contingency plan.
The document, which runs to more than 130 pages, outlines plans for 19 sectors should the UK leave the EU without a withdrawal deal.
It includes a move to purchase land at Dublin and Rosslare ports to deal with congestion caused by new custom checks.
Ireland's foreign minister said the plan was "stark" but "comprehensive".
The UK leaving the EU without a deal will cause significant stress to the Irish economy, Simon Coveney said.
His comments come as it emerged Theresa May's cabinet has decided to "ramp up" preparations for a no-deal amid uncertainty over the fate of the prime minister's proposed EU exit plan.
The UK government has allocated to ministers £2bn it had set aside in case Brexit happens on 29 March without a withdrawal deal being accepted by the Commons.
Mr Coveney, who is also the tánaiste (deputy prime minister), said the Irish government's preparations for a no-deal Brexit had now accelerated and that planning had been taking place for well over a year.
What does the document say?
The document, published by the Irish government, warned that Ireland's economy could be the "most adversely affected" out of all EU member states and that the country's security would also be "seriously impacted".
It said the Irish government is "now prioritising no-deal planning" and that any necessary no-deal legislation will be brought before the Dáil (Irish parliament) in January.
It outlines key plans including:
- A move to purchase extra land at ports in Dublin and Rosslare in County Wexford to handle congestion caused by new custom checks as well as measures to mitigate extra pressures on Dublin Airport
- Extra staff for departments including the Irish Revenue and the Department of Agriculture, Food and the Marine
- A commitment to maintaining law enforcement co-operation between the Republic and Northern Ireland
- A focus on ensuring uninterrupted air travel between the UK and the EU in the event of a no-deal scenario
The document also acknowledges concerns among sectors in Northern Ireland, such as farming and business, in the event of a no-deal Brexit, and indicates that the Irish government will "try to mitigate the effects to the extent possible, while recognising that this will be primarily a matter for the British government and the Northern Ireland authorities".
Mr Coveney said this was a working document that would be updated as weeks pass.
Speaking to reporters in Dublin, the tánaiste said Ireland was not engaged in contingency plans for the return of a hard border but that avoiding this would become "very difficult" in the event of a no-deal scenario.
Mr Coveney also said he was "very confident" that there would be no need to stockpile drugs in the event of a no-deal Brexit.
On the impact of a no-deal scenario on the UK, the tánaiste said it would take "a long time" to put in place a trading arrangement with the EU and this would be "very uncomfortable".
Tánaiste @simoncoveney speaking this evening about Ireland’s contingency planning for a no deal #Brexit: “The UK leaving is going to cause us a significant challenge in the first quarter next year. We have accelerated our planning which will involve multiple sectors.“ pic.twitter.com/kw886zW60o— MerrionStreet.ie (@merrionstreet) December 19, 2018
Earlier on Wednesday, taoiseach (prime minister) Leo Varadkar agreed to share his government's plans for a hard Brexit with opposition TDs (members of the Dáil) on Wednesday night, a day earlier than originally planned.