The Irish Aviation Authority has said it may have to impose a no fly zone over the Republic on Tuesday due to the volcanic ash cloud drifting south.
The IAA said the alert was based on current information from the Volcanic Ash Advice Centre (VAAC).
The VAAC will update the IAA at 2000 BST and a decison on reinstating the flight ban will be taken after that.
Irish carrier Aer Arann has cancelled its flights on Monday night from Dublin to City of Derry and Donegal airports.
The UK’s air traffic control body Nats is liaising with the Met office and expect to have more information at around 2100 BST.
Flights from the UK and Europe are not expected to be impacted on Tuesday. However flights originating from Irish and Northern Irish airports may be affected.
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,” Mr Brennan said.
“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.”
Flights over Europe were hit by a six-day shutdown of airspace last month over fears of the effect on jet engines of ash from a volcanic eruption in Iceland.