A new cloud of volcanic ash means flights are currently banned over Northern Ireland and parts of west Scotland, until 1pm.
The Icelandic volcano Eyjafjallajökull has seen an increase in activity, spreading a plume of ash across the Northwest of the UK and Ireland.
The ban is expected to be in place until at least 1pm this afternoon, and is affecting airports throughout Ireland, as well as flights to Argyll and the Hebrides in Scotland.
All flights to and from Dublin or Cork have been cancelled until at least 1pm.
All flights departing from Belfast International airport are cancelled until 4.30pm. Flights arriving into Belfast International are cancelled until at least 1pm. Belfast City Airport has also made cancellations.
Ryanair has cancelled all flights to and from Ireland until 2pm today. Some 2pm departures may run, but with delays, said the airline.
Aer Lingus has cancelled all its UK and European flights scheduled to depart and arrive into Dublin, Cork, Shannon and Belfast airports before 1pm.
NATS, the air navigation services provider, warned: "Conditions around the movement of the layers of the volcanic ash cloud over the UK remain dynamic."