Ireland, UK reopen skies after ash alert

Ireland and Britain re-opened their airspace on Tuesday after imposing a temporary flight ban due to the return of ash from an Icelandic volcano which paralysed Europe's skies last month.

But the ban prevented thousands of travellers from flying - including the Irish transport minister who was due in Brussels for EU talks on last month's chaos - while Irish authorities and one airline warned of possible further disruption.

The Irish Aviation Authority (IAA) and Britain's National Air Traffic Services (NATS) cleared flights to resume from 1:00 pm 1200 GMT (2200 AEST) after a suspension since late Monday over northwest Scotland and 0600 GMT (1600 AEST) in Ireland.

"The IAA has cleared Irish airports to open for full operations," it said in a statement.

"The situation will be reviewed as the week goes on. Winds are forecast to continue coming from a northerly direction for the next few days and this could lead to further problems."

In another warning of further problems, British-based budget airline easyJet said flights could be disrupted on Wednesday.

"The Met Office has advised airlines that the ash plume may reach Scotland airspace overnight. As a result this may cause disruption to flights to/from Scotland," said the airline in a statement.

As well as the Irish closure, Britain's Civil Aviation Authority (CAA) also announced the suspension of flights overnight above Northern Ireland and the Outer Hebrides, a group of islands off the west coast of Scotland.

But NATS later announced the lifting of the ban from 1200 GMT, "with the exception of a very small no-fly zone identified by the CAA in the northwest corner of UK airspace."

Airspace across Europe was closed for up to a week last month after the eruption of Iceland's Eyjafjoell volcano, but was re-opened after emergency talks between European governments, airlines and regulators.

In Reykjavik, experts said the new airport closures were due to a small, temporary hike in ash from the volcano at the weekend along with a change in wind direction.

"The ash plume temporarily increased a little on Sunday, but now it has decreased," Bryndis Brandsdottir, a geophysicist at the University of Iceland, told AFP.

The new alerts did not disrupt aircraft flying over Ireland from Britain or Europe, or southern British airports including Heathrow, Europe's busiest air hub, authorities in the two countries said.

But they triggered the cancellation of hundreds of flights in and out of Ireland and Northern Ireland, bringing fresh chaos to thousands of people.

One victim of the ban was Ireland's Transport Minister Noel Dempsey, who had to cancel a trip to Brussels for talks with his European Union counterparts on the recent ash cloud travel chaos.

Heathrow said that around 20 flights to and from the west London airport had been cancelled this morning.

"We are asking passengers to check with their airlines before coming to the airport," said a Heathrow spokeswoman.

Meanwhile Irish airline Aer Lingus said the flight ban last month had cost it about 20 million euros ($A28.07 million), while warning that "the final cost will depend on the actual level of customer claims."