A secret Government memo has starkly warned of "conflict at sea" and "blockades" in Irish waters in the immediate aftermath of a no-deal Brexit.
Cabinet ministers were given the dire warning as part of a confidential briefing from Tánaiste Simon Coveney.
The Irish Independent understands the memorandum also outlined how disruption at Dublin Port could undermine public confidence in the security of food and medicine supplies in Ireland, and lead to panic buying among consumers.
This would in turn deplete the stockpiles that have been built up by supermarkets and pharmaceutical companies in recent months.
Mr Coveney's briefing to the Cabinet contained some of the starkest warnings to date on the consequences of a no-deal Brexit, with just 21 days left and little indication from London or Brussels that an agreement is on the cards.
Ministers were last week warned over a failure to ensure Ireland has sufficient measures in place to assure the European Commission and other EU members that the bloc's single market is being protected. This would put the State's own single market membership at risk "with serious economic consequences" as a result.
The starkest warning related to areas that fall outside the control of the Irish Government, including the loss of access to UK fishing zones if there is a crash-out Brexit.
This could create a possible displacement of fleets of ships from other EU member states which normally use waters around the UK, and raises the potential for "conflict at sea and blockades", the confidential memo said.
The report, compiled by a civil servant heavily involved in the Brexit preparations, highlighted the potential for trouble at sea to seriously escalate at an early stage after October 31, and have a significant impact on the Irish fishing industry.
There were further warnings of the risk of significant delays and traffic disruption at Dublin Port - with impact on traffic outside the port - in the immediate period after Halloween, given the introduction of new checks and procedures. Disruption is likely due to trucks arriving at the ports with incomplete or no documentation, ministers were informed.
They were also given details of other factors outside the Irish Government's control, including possible decisions taken by UK and EU ports, ferry companies and protests by fishermen - all of which could also have a knock-on impact and result in delays.
Ministers were informed that disruption at Dublin Port or on the "UK Landbridge" - which is how much of Irish freight accesses mainland Europe and vice versa - could "undermine public confidence in the security of supply lines, in particular food and medicines" with the consequent risk of consumers panic buying and stockpiles being depleted.
The Cabinet was informed that risks remain both from the loss of public confidence and a lack of preparedness by businesses for a no-deal scenario.
The agri-food, fisheries, manufacturing and tourism sectors could all be affected directly by such disruption.
Mr Coveney's colleagues were also told that speculation about an extension to the Brexit deadline or a deal being achieved was posing challenges to ensuring there is a necessary level of preparedness and was feeding "reluctance" from some businesses to spend resources and make efforts to ensure they are ready for no deal.
The briefing about the potential risk to Ireland's single market membership comes amid negotiations between the Government here and the European Commission on what customs checks and controls will have to be carried out on goods entering the Republic from the North in the event of a UK crash-out.
Taoiseach Leo Varadkar has previously confirmed that there may be some checks that have to take place near the Border, but the Government has been reluctant to provide further details amid ongoing talks with the commission.
It is unlikely to confirm any plans until after next week's crucial European Council summit.
Mr Coveney has previously said not all customs and regulatory checks will come into force immediately after a no-deal Brexit.
There will be a timeline for their roll-out that will have to be agreed with the commission. "For pragmatic reasons, all of this is not going to be done by the end of October," he told the 'Sunday Independent' last month.