Thick drifts of volcanic ash blanketed parts of rural Iceland as a vast, invisible plume of grit drifted over Europe, emptying the skies of planes and sending hundreds of thousands in search of hotel rooms, train tickets or rental cars.
Meanwhile Polish officials feared the ash cloud could threaten the arrival of world leaders for tomorrow's state funeral of President Lech Kaczynski and his wife Maria in the southern city of Krakow.
The couple were killed in a plane crash last Saturday in western Russia, along with 94 others among Poland's political and military elite.
So far, US president Barack Obama, Russian president Dmitry Medvedev and German chancellor Angela Merkel are among those coming to the funeral and no-one has cancelled.
Mr Kaczynski's family insisted yesterday they wanted the funeral to go ahead as planned, but there was no denying the ash cloud was moving south and east.
Air traffic agency Eurocontrol said almost two-thirds of Europe's flights were cancelled yesterday as airspace remained largely closed in Britain and across large chunks of north and central Europe.
"The skies are totally empty over northern Europe," said Brian Flynn, deputy head of Eurocontrol, adding "there will be some significant disruption of European air traffic tomorrow".
The agency said about 16,000 of Europe's usual 28,000 daily flights were cancelled yesterday - twice as many as those cancelled a day earlier.
US airlines cancelled 280 of the more than 330 transatlantic flights of a normal day, and about 60 flights between Asia and Europe were axed.
The International Air Transport Association said the volcano was costing the industry at least €95m a day.
Southern Iceland's Eyjafjallajokull glacier began erupting for the second time in a month on Wednesday, sending ash several miles into the air. Winds pushed the plume south and east across Britain, Ireland, Scandinavia and into the heart of Europe.
Grey ash settled in drifts near the glacier, swirling in the air and turning day into night. Authorities told people in the area with respiratory problems to stay indoors and advised everyone to wear masks and protective goggles outside.
In major European cities, travel chaos reigned. Extra trains were put on in Amsterdam and lines to buy train tickets were so long that the rail company handed out free coffee.
Eurostar said it was carrying almost 50,000 passengers between London, Paris and Brussels. Thalys, a high-speed venture of the French, Belgian and German rail companies, was allowing passengers to buy tickets even if trains were fully booked.
Ferry operators in Britain received a flurry of bookings from people desperate to cross the channel to France, while London taxi company Addison Lee said it had received requests for journeys to cities as far away as Paris, Milan, Amsterdam and Zurich.
The disruptions hit tourists, business travellers and dignitaries alike.
Mrs Merkel had to go to Portugal rather than Berlin as she flew home from a US visit. Norwegian prime minister Jens Stoltenberg managed to get a flight to Madrid from New York, but was still not sure when or how he would get back home.
The military also had to adjust. Five German soldiers wounded in Afghanistan were diverted to Turkey instead of Germany, while US medical evacuations for troops in Iraq and Afghanistan are being flown directly from the warfronts to Washington rather than Germany.
The US military has also stopped using temporarily closed air bases in the UK and Germany.
Aviation experts said it was among the worst disruptions Europe had seen.
In Iceland, torrents of water carried away chunks of ice the size of small houses on Thursday as hot gases melted the glacier over the volcano. Sections of the country's main ring road were wiped out by the flash floods.
More floods from melting waters are expected as long as the volcano keeps erupting - and in 1821, the same volcano managed to erupt for more than a year.
Iceland, a nation of 320,000 people, sits on a large volcanic hotspot in the Atlantic's mid-oceanic ridge and has a history of devastating eruptions. One of the worst was the 1783 eruption of the Laki volcano, which spewed a toxic cloud over Europe, killing tens of thousands.
Australia's Qantas airline cancelled all flights to Europe today and said it was not known when they would resume.