Parts of the airspace over Britain and Northern Ireland will close on Tuesday and operations from Irish airports will be restricted because of the cloud of volcanic ash drifting south from Iceland that wreaked havoc on European air travel last month.
Britain's Civil Aviation Authority (CAA) said it had imposed no-fly zones over parts of Scotland and will close Northern Irish airspace from 0600 GMT on Tuesday due to rising levels of volcanic ash in the atmosphere.
"Because ash concentrations exceed the levels agreed as safe by engine manufacturers, airspace over the Outer Hebrides was closed to all operations from 1800 ...(1700 GMT on Monday) following Met Office (weather service) advice," the CAA said on its website.
"Following the latest update from the Met Office, airspace over Northern Ireland will also be closed from 0700 local time...(0600 GMT on Tuesday)," it said.
The restrictions will close Belfast and Derry airports, it said.
Flights over Europe were hit by a six-day shutdown of airspace last month over fears of the effect on jet engines of ash from the volcanic eruption in Iceland.
The Irish Aviation Authority (IAA) said it would impose restrictions on all flights in and out of Ireland from 0600 GMT until 1200 GMT due to risk of ash ingestion in aircraft engines.
But overflights of Ireland from the United Kingdom and Europe will not be affected while flights in mainland Europe will operate normally, it said.
The IAA said information from the Volcanic Ash Advice Centre suggested the no-fly zone would affect Dublin, Shannon Galway, Sligo, Ireland West, Donegal, Cork and Kerry.
The CAA and IAA said they would review the situation following the latest weather reports on Tuesday morning.