The Irish Aviation Authority has said it will lift restrictions at Dublin Airport at 4am.
The airport has been closed since 11am this morning due to the ash cloud from the Eyjafjallajokull volcano in Iceland.
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The IAA said the ash cloud is moving southwestwards and 'airport restrictions will be lifted according to its progress'.
Elsewhere, the airports in Cork, Waterford, and Donegal will also re-open at 4am, while Sligo airport will begin operations at 6am.
Shannon Airport and the airports in Knock and Galway will be closed until 8am, while Kerry airport will remain closed until 9am.
The IAA said it 'appreciates the difficulties facing passengers and airlines at this time'. It added that decisions are taken solely on the grounds of safety.
It said intending passengers should continue to contact their airline's website to establish the up-to-date position on flight schedules.
The authority will issue its next statement on the disruption at 10am tomorrow morning unless 'circumstances change significantly' tonight.
Overflights of Irish airspace between North America and Europe will continue as normal.
Aer Lingus has confirmed that it plans to operate its full transatlantic schedule from Ireland to the US tomorrow.
It intends to operate the majority of its short-haul services, however some disruption is anticipated.
Ryanair has cancelled four flights tomorrow into and out of Shannon and Kerry airports.
It expects all flights to operate as normal from Dublin, Cork and Knock, as well as airports in the UK.
Belfast International Airport and George Best Belfast City Airport will be closed until 1am.
