The Irish Aviation Authority (IAA) has warned that Dublin, Shannon and some regional northern airports may see flight restrictions tomorrow.
North easterly winds are causing the volcanic ash cloud to drift south and, potentially, back into Irish airspace.
"Current information from the Volcanic Ash Advice Centre (VAAC) suggests that a no-fly zone may have to be imposed over Ireland tomorrow that may affect Dublin, Shannon and some regional airports," the IAA said in a statement.
The IAA expects a further update from the VAAC at 8pm and will make a decision then concerning operations at Irish airports and Irish airspace.
Over-flights of Ireland from the UK and Europe are not expected to be impacted tomorrow and southern UK Airports (Heathrow etc ) are not expected to be impacted. Flights originating from Irish airports may be affected.
Those intending to travel have been advised to contact their airlines' websites after 8.30pm for information.
Eamon Brennan, IAA chief executive, said winds have already pushed part of the volcanic ash cloud down over part of the centre of Ireland.
“The latest information we have is that some of the denser volcanic ash, that’s the no-fly zone, is over the Donegal area and we are concerned about the north-easterly winds moving this down over the rest of the country,” he told RTE radio.
“At the moment we have a slither of denser ash over the midlands and if this continues for the next number of hours we have no option, based on the new regime imposed in Europe last week, except to impose a no-fly zone and a 60-mile buffer zone which would effectively close Shannon and Dublin airports.”
Mr Brennan said even though emissions from the volcano have been low over the last number of days, the cloud which has drifted south could impact on Ireland and the western part of the Scottish Isles.
He revealed the plume was sitting 20,000 feet over parts of the country, adding that weather conditions were not favourable.
“We expect all flights this evening to continue as normal except we expect Donegal airport to close early,” he added.
“All other airports in the Republic will operate as normal right in to tonight. The issue that we have is that the latest predictions shows this pushing southwards over night and we will be able to make a call on this at 8.30pm.”