European governments opened the continent's airspace to new flights from Tuesday giving hope to passengers around the world trapped by the cloud of volcano ash that has grounded airlines there.

But British air traffic chiefs warned that the Icelandic volcano at the source of the chaos had spewed a fresh cloud of ash that was headed for Britain.

On Monday, as the dust that has blanketed much of Europe's skies forced the cancellation of another 20,000 flights, Britain sent navy ships and other governments took their own measures to rescue stranded passengers.

But under relentless pressure from airlines who have lost more than a billion dollars from the crisis so far, EU transport ministers agreed to ease restrictions from Tuesday.

"From tomorrow morning on, we should progressively see more planes start to fly," EU Transport Commissioner Siim Kallas said Monday.

Europe's air traffic control group Eurocontrol subsequently predicted that flights over the continent could be running normally again by Thursday.

France said it was progressively reopening its airports, with restricted flights from Paris to start from early Tuesday.

And although flights over Germany remained banned until 1200 GMT Tuesday, some operated with special permission. German flag carrier Lufthansa on Monday announced the immediate resumption of all its long-haul flights.

KLM said it would be flying in and out of Amsterdam Tuesday, after three of its flights left Amsterdam-Schiphol airport Monday for Shanghai, Dubai and New York.

Flights heading for Europe from New York's John F. Kennedy airport also started to run again late Monday.

Authorities in Sweden, Croatia, Hungary and the Czech Republic announced flights were resuming. Romania and Bulgaria announced their airspace had been reopened, while Switzerland said its airspace would reopen early Tuesday.

But hopes that the ash cloud nightmare might be over were tempered by the latest bulletin from British aviation chiefs Tuesday.

"The volcano eruption in Iceland has strengthened and a new ash cloud is spreading south and east towards the UK," said the National Air Traffic Services (NATS), which manages British airspace.

That made it less likely London airports would be reopened Tuesday, as had been hoped, although plans to open airspace in Scotland should still go ahead, said the air authority.

The problem meanwhile had spread west across the Atlantic, as Canada's Saint John's, Newfoundland announced it had cancelled a batch of domestic flights because of fears the ash would reach their airspace.

On the other side of the world, Australia warned travellers Tuesday that hotel accommodation in Asian transport hubs was limited because of the air travel crisis.

"Travellers departing Australia on Europe-bound flights may experience difficulties obtaining accommodation in transit hubs such as Singapore, Bangkok and Hong Kong," said a message on the foreign ministry's website.

In Europe, marooned passengers juggled rail, boat and road links, in a bid to get home.

Britain ordered its flagship aircraft carrier HMS Ark Royal and HMS Ocean and HMS Albion to pick up thousands of Britons from France - where they have come from all over Europe - and from Spain.

And Spain, one of the rare countries operating normally, has struck an agreement with Britain, France and Germany to fly hundreds of thousands of their nationals back to Europe via Spanish airports.

Nearly seven million passengers have been affected by the blanket shutdowns, which governments have insisted were essential on safety grounds, given the possibility that the ash could choke up jet engines and provoke air disasters.

But the airlines have criticised EU leaders for their handling of the chaos sparked by Iceland's Eyjafjoell volcano, which began erupting last Wednesday.

"This is a European embarrassment and it's a European mess," said Giovanni Bisignani, director general of the International Air Transport Association (IATA).

But as airlines argued their case, a senior US military official said the ash had affected one of NATO's F-16 fighter planes, which detected a glass build-up inside its engine.

Ash from volcanoes can be turned into a glass form at high temperatures when it passes through a jet engine.

Companies are losing 200 million euros (270 million dollars) per day according to IATA.