Most of Europe's airspace will remain closed to all but emergency flights until at least Friday evening due to the dangers posed by clouds of volcanic ash from Iceland, according to aviation officials.

The volcano began erupting on Wednesday for the second time in a month from below the Eyjafjallajokull glacier, hurling a plume of ash six to 11 kilometers (four to seven miles) into the atmosphere.

Volcanic ash contains tiny particles of glass and pulverized rock that can cause dangerous malfunctions by damaging engines and airframes.

Tens of thousands affected

Most major airports in Germany were closed on Friday, including Hamburg, Leipzig, Duesseldorf and Berlin.

At the main Frankfurt airport - Europe's second busiest - an official statement said all flights had been cancelled from 8 a.m. local time onwards.

In addition, all European flights would be prevented from landing in Frankfurt on Friday, except for emergencies. Flights already in the air are to be rerouted to Munich, according to the statement.

French officials said on Friday that all flights at 25 of the country's airports - including Charles de Gaulle in Paris - had been cancelled.

A spokesman at Heathrow, Europe's busiest airport, said all flights had been cancelled until 18:00 local time on Friday, disrupting well over 200,000 passengers. More than 120,000 other passengers were affected at London's other two airports, Gatwick and Stansted.

Disruptions could linger

The Association of British Insurers said volcanic eruptions were not always covered by travel insurance for cancellation and delay, but some airlines issued statements confirming they would refund fares or change flights.

Scientists said the ash did not pose any health threat because it is at such a high altitude.

Bill McGuire, professor at the Aon Benfield UCL Hazard Research Center, said if the volcano continued erupting for more than 12 months, as it did the last time, periodic disruptions to air traffic could continue.

"The problem is volcanoes are very unpredictable and in this case we have only one eruption to go on," McGuire said.

"A lot depends on the wind. I would expect this shutdown to last a couple of days. But if the eruption continues - and continues to produce ash - we could see repeated disruptions for the next six months," he added.

glb/Reuters/AP
Editor: Martin Kuebler