All flights in and out of Northern Ireland’s three airports have been cancelled until 1900 BST due to the return of the volcanic ash cloud.
The Irish Aviation Authority has closed airports in Sligo, Donegal and Knock.
Dublin and Shannon airports are expected to remain open until at least 1400 BST.
Passengers who are due to travel on Sunday should check with their airline or tour operator before travelling to the airport.
In a statement, Ryanair said it expected Dublin, Kerry, Shannon and Cork Airports to remain open until at least 1900 BST.
Irish Aviation Authority (IAA) Chief Executive Eamonn Brennan said there is a strong possibility of other airport closures in the Republic on Sunday.
"The IAA is currently carrying out observation flights at a number of altitudes and is in discussion with other aviation authorities, airlines and engine manufacturers to assess the results of the tests in the interest of passenger safety.
"The authority will continue to review analysis and observation results throughout the day."
Forecasts say the ash may extend over the UK on Monday and Tuesday.
Jonathan Astill, from the air traffic authority, Nats, said: "Unfortunately, yet again, a mixture of volcanic activity and weather systems have conspired to bring a cloud of ash down towards the UK.
"As a result we’ve now got a cloud of high density volcanic ash rapidly encroaching on Northern Ireland and the Isle of Man."
EasyJet said it has so far cancelled 11 Sunday flights from Belfast International Airport.
The cloud is expected to lie over the London area by Tuesday, but is likely to have drifted out of UK airspace by Wednesday, forecasters say.
Prof Brian Golding, head of forecasting research at the Met Office, said the cloud stemmed from an eruption on Thursday.
"The volcano has now dropped back in height. It did that yesterday, so the ash coming towards us for the future isn’t quite so deep as it was on Thursday.
"It isn’t going to turn into a huge area and it’s being blown eastwards, between south-east and east. "
Ash from the Eyjafjallajokull volcano has caused disruption to thousands of flights since April.
The Department of Transport, which is establishing five-day ash prediction charts, is warning there is a chance airports in south-east England may be also be affected in the next few days.
Five day forecasts
Transport Secretary Philip Hammond said the situation was "fluid" but passenger safety was the top priority.
Ministers agreed on Saturday that the five-day forecasts, rather than 18-hour ones, would be made available on the Met Office website.
The Met Office said its charts would be updated every six hours. A spokeswoman said the ash plume was currently about 25,000ft (7,620m) high, with winds blowing from the north west.
But she said the wind was expected to change direction in the middle of next week, taking ash away from the UK.
In April, airspace across Europe was shut down for five days over concerns ash could turn to molten glass in high temperatures, crippling plane engines.
Scientists and engineers have since revised the safe-to-fly threshold, but clouds of volcanic ash have continued to drift over Europe, causing airport closures, flight delays and cancellations.
Airline fined
In the past week, several airports in southern Europe have been forced to close and flights have been re-routed.
Meanwhile, Italy has fined Ryanair 3m euros (£2.5m) for failing to help some passengers after cancelling their flights during the crisis.
Italy’s civil aviation authority fine on Ryanair comes after it said it knew of 178 cases of passengers who did not receive mandatory assistance, such as food – required under EU regulations – between 17 and 22 April. Ryanair called the allegation "complete rubbish".
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