A huge ash cloud from an Icelandic volcano turned the skies of northern Europe into a no-fly zone on Thursday, stranding hundreds of thousands of passengers.
The European air safety organisation said the disruption, the biggest seen in the region, could last another two days and a leading volcano expert said the ash could present intermittent problems to air traffic for 6 months if the eruption continued.
Even if the disruption is short lived, the financial impact on airlines could be significant, a consultant said. The International Air Transport Association had said only days ago airlines were slowly coming out of recession.
The volcano began erupting on Wednesday for the second time in a month from below the Eyjafjallajokull glacier. It hurled a plume of ash six to 11 kilometres (4 to 7 miles) into the atmosphere, and this spread south east overnight.
Volcanic ash contains tiny particles of glass and pulverised rock which can damage engines and airframes and an Icelandic volcanologist said on Thursday the eruption was growing more intense.
Britain barred flights in its air space, except in emergencies, until at least 0600 GMT on Friday, with a flight returning soldiers from Afghanistan having to be held in Cyprus.
It was the first time within living memory that a natural disaster had caused such a halt, a spokeswoman for Britain's National Air Traffic Service (NATS) said. Even after the September 11, 2001 attacks, Britain did not close its air space.
John Strickland, director of air transport consultancy JLS Consulting, saw possible broader hazards.
"Iceland sits right on one of the key routes between Europe and the USA and... depending on meteorological conditions it could also affect flights from Europe to Asia so there are two big international flows which could be affected by this."
FURTHER 48 HOURS
French authorities said they would close 24 airports across northern France before the end of Thursday, including in Paris. Brussels, Amsterdam and Geneva airports said they had cancelled a large number of flights and Eurocontrol spokesman Brian Flynn said the problem could persist for a further 48 hours.
Finland closed all airports except Helsinki-Vantaa.
The Association of British Insurers said volcanic eruptions were not always covered by travel insurance for cancellation and delay. But some airlines issued statements confirming they would refund fares or change flights.
Airline staff at Stansted airport, north-east of London, told customers it could be closed until Sunday, said stranded passenger Andy Evans.
"People just don't know what to do," he said. "There are hundreds of people in the queues at the sales desks."
A spokesman at Heathrow, Europe's busiest airport, said 840 out of 1,250 flights on Thursday were affected, disrupting about 180,000 passengers. More than 120,000 other passengers were affected at Gatwick, Stansted and Glasgow airports.
"There is a big financial impact on the airlines," said Strickland of JLS consulting. "We are now looking at at least a day's business wiped out for the airline business ... even if things were meteorologically fine to fly tomorrow by that time the airlines will have all their aircraft and crew out of position so they have no choice but to cancel further flights."
In 1982 a British Airways Boeing 747 lost power in all its engines when it flew into an ash cloud over Indonesia, gliding towards the ground before it was able to restart its engines.
The incident prompted the aviation industry to rethink the way it prepared for ash clouds, resulting in international contingency plans activated on Thursday.
Scientists said the ash did not pose any health threat because it is at such a high altitude.
Bill McGuire, professor at the Aon Benfield UCL Hazard Research Centre, said if the volcano continued erupting for more than 12 months, as it did the last time, periodic disruptions to air traffic could continue.
"The problem is volcanoes are very unpredictable and in this case we have only one eruption to go on," he said. "And a lot depends on the wind. I would expect this shutdown to last a couple of days. But if the eruption continues -- and continues to produce ash -- we could see repeated disruption over six months or so."
Brian Flynn, deputy head of operations at Eurocontrol, said the disruption was already unprecedented: "The extent is greater than we've ever seen before in the EU."
"The meteorological situation is such that the volcanic ash is progressing very slowly eastwards but there is not a lot of wind... so it is very slow and very dense."
Russian Prime Minister Vladimir Putin was forced to cancel a trip to Russia's Arctic town of Murmansk on Thursday. "The cloud has covered the entire region," said Putin's spokesman.
The eruption has grown more intense, University of Iceland volcanologist Armannn Hoskuldsson said.
To the east of the volcano, thousands of hectares of land were covered by a thick layer of ash, while a cloud was blotting out the sun in some areas along the southern coast of Iceland, local media reported.