One expert said the eruption could abate in the coming days, but a government spokesman said ash would keep drifting into the skies of Europe.

The thick, dark brown ash cloud has shut down air traffic across northern Europe and restrictions remained in place in many areas. However, Norway said it had resumed some limited flights in the north of the country.

"It is more or less the same situation as yesterday, it is still erupting, still exploding, still producing gas," University of Iceland professor Armann Hoskuldsson told Reuters.

"We expect it to last for two days or more or something. It cannot continue at this rate for many days. There is a limited amount of magma that can spew out," he added, saying it was the magma, or molten rock beneath the Earth's surface, coming out of the volcano that turned into ash.

Environment Ministry spokesman Gudmundur Gudmundsson agreed.

"The eruption is ongoing and we are not expecting any change in the production of ash...High level winds will keep dispersing the plume over Europe," he said.

The eruption has taken place under the Eyjafjallajokull glacier, normally a popular hiking ground in southern Iceland.

Another professor said on Thursday that the heat had melted up to a third of the glacial ice covering the crater, causing a nearby river to burst its banks.

Icelandic radio said part of the ring road that goes around the small north Atlantic island had been swept away.

To the east of the volcano, thousands of hectares of land are covered by a thick layer of ash.

The cloud of ash from the eruption has hit air travel all over northern Europe, with flights grounded or diverted due to the risk of engine damage from sucking in particles of ash from the volcanic cloud.

The volcano under the Ejfjallajokull glacier, Iceland's fifth largest glacier, has erupted five times since Iceland was settled in the ninth century.

Iceland sits on a volcanic hotspot in the Mid-Atlantic Ridge and has relatively frequent eruptions, although most occur in sparsely populated areas and pose little danger to people or property. Before March, the last eruption took place in 2004.