A cloud of volcanic ash from Iceland continued to drift over the North Atlantic and parts of Europe today, prompting air traffic authorities in Germany, Austria, Spain and Italy to close parts of their airspace.
The ash cloud also hindered flights to and from Ireland, France and Portugal.
While Ireland's largest airports remained fully operational today, smaller airports along the west coast were restricted from this afternoon.
Eurocontrol said the volcanic ash from the Eyjafjallajökull volcano is "substantially" affecting European airspace and at least 500 flights have been cancelled.
A shutdown of European airspace last month because of ash from the volcano grounded more than 100,000 flights and cost carriers over €1 billion, according to the International Air Transport Association.
The Irish Aviation Authority said Dublin, Cork and Waterford airports will remain open until at least 1pm tomorrow. Shannon will remain open until 7am. Donegal, Sligo and Knock were restricted from 3pm today, and Galway was affected from 4pm. Kerry airport will be restricted from 10pm.
The IAA said the Eyjafjallajökull volcano is still moderately active. It warned an expected change in the direction of the wind by late tonight could push the ash plume, currently to the west, back over Ireland.
The authority is in constant contact with the Volcanic Ash Advisory Centre (VAAC) and the Central Flow Management Unit (CFMU) at Eurocontrol, and is monitoring the path of the huge ash cloud in order to assess the impact it could have on air safety.
“Passengers planning to travel by air over the coming days are advised to regularly check their airline websites and the IAA website in advance of going to the airport,” it said.
Italy closed a large part of its airspace in the north of the country, the civil aviation authority ENAC said. Milan, Pisa and Florence airports were closed, though Venice, Trieste and Rimini remained open.
In Geneva, dozens of flights to Ireland, Britain, Portugal, Spain, France and Hungary were cancelled, while Zurich airport listed flights to Washington, Dublin and Porto as cancelled. Geneva airport is one of the main hubs for budget carrier easyJet. The airline warned passengers today to expect further disruption to flights operating to and from Switzerland, southern and central France, northern Italy and northern Portugal.
Weather forecasts predicted that the ash would spread to southern parts of Germany, the Czech Republic and Austria by tonight. Germany's air safety authority closed airspace over Munich and southern parts of the country this afternoon as a precautionary measure.
The French aviation authority said some 30 flights from Paris to southern Europe were cancelled, although most French airspace and airports remained open today after a test flight by Air France yesterday found no ash.
Separately, a finger of the main ash cloud - centred in the mid-Atlantic at altitudes of up to 10,000 metres - was still touching on parts of Portugal and Spain, forcing the closure of airports at Porto, La Coruna, Vigo, and Santiago.
Some small Scottish airports were closed this morning due to the ash cloud, Highland and Islands Airports Limited said. It said Barra, Benbecula, Kirkwall, Inverness, Stornoway and Tiree airports are expected to be shut until this afternoon.
Flights to and from the Canary Islands were badly affected yesterday. Ryanair said it was putting on extra flights today and tomorrow to and from Fuerteventura, Gran Canaria, Lanzarote and Tenerife, to and from Ireland and the UK.
Aer Lingus chief executive Christoph Mueller said the airline has so far sent more than a half a million text messages to passengers notifying them of cancelled flights. In a statement, he thanked customers for their patience "We will continue to do all in our power to get as many of our customers to their intended destinations as we possibly can and to keep all customers updated with the latest information," he said. "We thank all of our customers most sincerely for their patience and support throughout this difficult time."
Eurocontrol, the Brussels-based agency that coordinates air traffic control centres throughout the continent, said transatlantic flights will continue to be diverted northward over Greenland to avoid the cloud stretching from Iceland to the Azores Islands. It warned airlines to plan on taking on more fuel for the longer flight around the oceanic no-fly zone.
On Wednesday, an area of low pressure over Iceland is expected to take the ash away from the Ireland.