Aviation chiefs predicted Thursday that the drifting dust could throw travel plans into disarray for a further two days, after flights were banned over more than 10 European countries.

Thousands of passengers from Hong Kong to Dublin were stranded when aviation chiefs decided it was too risky to allow planes to fly through the cloud of ash, which is upwards of 20,000 feet (6,000 metres) above the earth’s surface.

Although not visible from the ground, volcanic ash can be highly dangerous for aircraft, clogging up the engines and reducing visibility, experts say.

Up to 5,000 flights were affected by the flight bans Thursday, said Eurocontrol, the agency that coordinates flights in Europe.

Flights from all over the world, including Tokyo, Hong Kong, Dubai, Paris and Athens, were affected by the cancellations in northern Europe.

The ash from the volcano under Iceland’s Eyjafjallajokull glacier blew southeast after Wednesday’s eruption towards Scotland and Norway, before covering England and Scandinavia, according to the London-based Volcanic Ash Advisory Centre.

The drifting cloud also closed airspace in Belgium, Denmark, Finland, Ireland, the Netherlands, Norway, Sweden, the north of France, parts of northern Germany and part of northern Poland.

Passengers’ travel nightmare was far from over Friday, with airspace closures still in force and the European air traffic control group Eurocontrol predicting further travel chaos.

The disruption “could last two days,” spokesman Kyla Evans told AFP from the agency’s Brussel’s headquarters.

Flights between North America and Europe also faced major disruption, with half of all services expected to be cancelled Friday, according to Eurocontrol.

Farmer tells of Iceland volcano blast There are an average of 600 flights between Europe and North America a day, it said.

Britain — which closed its airspace at 1100 GMT Thursday — said the ban would stay in force until 1800 GMT Friday for most flights in its airspace.

Belgian airspace is to remain closed Friday, authorities confirmed, while Air France said its flights in and out of Paris would not run.

In Scotland, health authorities warned people to beware of possible health problems from volcano ash falling to the ground.

Norway was the first to ground its flights on Wednesday evening, followed by Scotland overnight into Thursday and then London, before air traffic controllers announced no flights could go through British and Irish airspace.

Finland closed its northern airspace an hour later, followed by Denmark and Sweden.

Paris’s two main airports and more than a dozen others in the north of France were closed Thursday, aviation officials said.

A total of 466 flights between Spain and European destinations were cancelled Thursday because of the ash by 1530 GMT, Spain’s AENA aviation authority said.

Icelandic airports, however, reported no problems.

“The wind is blowing the ash to the east,” Hjordis Gudmundsdottir of the Icelandic Airport Authority told AFP, adding: “It’s amazing really.”

About 300 flights in and out of London’s Heathrow and Gatwick airports had already been cancelled before the airspace was closed, leaving many of the 260,000 passengers who typically use the airports each day with nowhere to go.

“Basically we’re stranded here, and a lot of people are angry. I realise it’s an act of God — however it would be nice to have another exit strategy,” said Isobel Connolly, who was due to fly from Heathrow to Ireland.

In 1982, British Airways and Singapore Airways jumbo jets lost their engines when they flew into an ash cloud over Indonesia, while a KLM flight had a similar experience in 1989 over Alaska.

“On each occasion, the plane fell to within a few thousand feet of the ground before it was possible to restart the engines,” Rothery said.