The Irish Aviation Authority (IAA) has said Irish airspace will close from 7am tomorrow because of an ash cloud drifting down from Iceland.
The decision will be reviewed at 1pm tomorrow.
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Intending passengers are advised to check their airline's website for more information.
Donegal Airport closed earlier and two Aer Arann flights were cancelled.
Almost 440 flights were due to depart and fly into Dublin Airport throughout the day, with more from Shannon, Cork and regional airports.
Over-flights of Ireland from the UK and Europe will not be impacted, the IAA said, adding flights in mainland Europe will operate normally.
Earlier, IAA chief executive Eamonn Brennan said winds had 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 RTÉ 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.’
Aer Lingus later confirmed that all its UK and European flights scheduled to depart and arrive into Dublin, Cork, Shannon and Belfast airports, prior to 1pm tomorrow, have been cancelled.
Aer Lingus plans to operate all its flights to the US with the exception of EI 105 from Dublin to New York. Customers are advised that there may be delays to transatlantic flights.
Ryanair have advised passengers due to travel on flights to and from Ireland between 6am and 1pm not to go to the airport.
Scotland also facing disruption
The skies over parts of Scotland have also been closed, Britain’s Civil Aviation Authority (CAA) said tonight.
The ash is forecast to exceed the safe level agreed by the CAA and airlines in the Outer Hebrides tomorrow.
Airspace over the Outer Hebrides was closed to all operations at 6pm following advice from Britain's Met Office.
The closures could see flights to and from the Western Isles cancelled tomorrow, but the situation will be constantly reviewed.
Passengers are advised to check with their airline before travelling.