Ash cloud blocks 17,000 flights

Authorities say 17,000 flights to and around Europe are set to be cancelled because of a dangerous cloud of ash spreading from an Icelandic volcano.

The 10km high plume of ash has closed huge swathes of European airspace - the continent's biggest air travel shutdown since World War II.

Experts warn the fallout from the Eyjafjallajokull volcano could take several days to pass and aviation authorities have refused to say when the skies would clear again.

The cloud now extends from the Atlantic to the Russian capital and from the Arctic Circle to Austria and Bulgaria in southern Europe.

Eurocontrol, the air traffic coordinating agency, has warned there is more travel misery to come for travellers in Europe and beyond in the next few days.

"Forecasts suggest that the cloud of volcanic ash is continuing to move east and south-east and that the impact will continue for at least the next 24 hours," it said.

Passengers stranded

Eurocontrol "expects around 11,000 flights to take place today in European airspace. On a normal day, we would expect 28,000".

Thousands of people are stranded in airports around the world as a global flight backlog builds up.

Europe's three biggest airports - London Heathrow, Paris-Charles de Gaulle and Frankfurt -have been forced to close by the ash, which is a threat to jet engines and visibility.

Poland, Britain, Austria, the Czech Republic, Denmark, Lithuania, Latvia, Estonia, Belgium and the Netherlands have shut down all or most of their airspace.

Finland, France, Germany, Russia and Spain have experienced major disruption, although Sweden and Ireland are gradually reopening their airspace, and Norway has temporarily allowed some flights as the ash drifted away.

Flights scrapped

Qantas has scrapped flights to London and Frankfurt, and hundreds of passengers are stranded in airports in Asia waiting for connecting flights that have been cancelled.

Debbie Eidsforth, 36, spent the night at Heathrow and was trying to get back to Adelaide via Hong Kong.

"I had paid 5,500 pounds ($US8,500) for my flights, but it doesn't matter what class you fly in, everyone's in the same situation," she said.

Thousands of extra passengers have swamped Eurostar's train services from London to mainland Europe, as travellers rush to find alternative methods of transport.

The company said 10,000 more travellers than usual had attempted to book Eurostar seats out of Paris on Friday, almost a third more than would normally have been expected.

Ash risk to planes

Three extra trains have been laid on, but queues are building at Paris's Gare du Nord station.

The volcano under the Eyjafjallajokull glacier has been spewing ash for several days - and experts say it may continue to do so periodically for up to six months.

Volcanic ash can be harmful to plane engines, potentially causing them to lose power during flight.

In the past 20 years, there have been 80 recorded encounters between aircraft and volcanic clouds, causing the near-loss of two Boeing 747s with almost 500 people on board and damage to 20 other planes, experts said.

Australians stranded overseas needing consular assistance can contact the nearest Australian diplomatic mission or the consular emergency centre on +61 2 6261 3305.