Airline industry association Iata criticised Europe's response to a volcanic ash cloud and called on Monday for urgent steps to reopen airspace after five days of closures that have cost airlines $250 million a day.

Iata head Giovanni Bisignani said authorities in Europe had 'missed opportunities to fly safely'.

'This volcano has crippled the aviation sector, firstly in Europe and is now having worldwide implications. The scale of the economic impact (on aviation) is now greater than 9/11 when US airspace was closed for three days,' Bisignani said, referring to the Sept. 11 2001 attacks in the United States.

'We must move away from this blanket closure and find ways to flexibly open air space, step by step,' he told a news briefing in Paris.

European transport ministers are due to discuss the airspace crisis at 1300 GMT, after a meeting of the European aviation control agency Eurocontrol, and officials hope flights will increase significantly.   

From just over a fifth of flights taking to the air on Sunday, the figure could rise to up to a half on Monday, said the officials. Austria opened their airports on Monday, but other countries kept no-fly decrees in place. Italy re-closed its northern airspace after briefly opening it on Monday.   

The closure of most of Europe's airspace because of a huge cloud of ash from an Icelandic volcano stranded millions of passengers, and importers and exporters have been hit.

The crisis has had a knock on effect across the world and its impact on everyday life in Europe has deepened. In Britain, companies reported staff had been unable to get back from Easter holidays abroad and hospitals said they were cancelling some operations because surgeons were stuck in far off places.

Bisignani called for urgent action to safely re-open airspace and called for a meeting of the International Civil Aviation Organization, the United Nations aviation body.

'We have to make decisions based on the real situation and not on theoretical models. They (the authorities) have missed opportunities to fly safely,' he said.

A senior European Union official said on Sunday the current situation was not sustainable, as airlines called for a review of no-fly decrees after conducting test flights at the weekend without any apparent problems from the ash cloud.   

'We cannot wait until the ash flows just disappear,' said EU Transport Commissioner Siim Kallas, adding he hoped 50 percent of European airspace would be risk-free on Monday.

Only 5,000 flights took place in European airspace on Sunday, compared with 24,000 normally, Eurocontrol, the European aviation control agency said. Since Thursday 63,000 flights have been cancelled.   

Dutch airline KLM, which has flown several test flights, said most European airspace was safe despite the plume of ash, and dispatched two commercial freight flights to Asia on Sunday.

Volcanic ash is abrasive and can strip off aerodynamic surfaces and paralyse an aircraft engine. Aircraft electronics and windshields can also be damaged.        

Senior Eurocontrol official Brian Flynn said the International Civil Aviation Organisation published rules that needed to be adhered to worldwide, and guidelines to interpret at continental level.

'One could say that the guidelines are interpreted slightly more rigorously in Europe than in the United States, when it comes to responsibilities of air traffic control agencies and pilots,' he told Reuters. - Reuters