Iceland's most active volcano erupted on Saturday, just a year after another eruption on the island shut down European air traffic and caused travel chaos for days.
Huge clouds of smoke could be seen in the air spurting from the Grimsvotn volcano, followed by a series of small earthquakes.
A no-fly zone was immediately designated for 120 miles (220 kilometres) in all directions from the eruption.
A spokesman for Iceland's air traffic authority said the flight ban was a precautionary measure until the full extent of the problem was known.
Icelandic Met Office geologist Hjorleifur Sveinbjornsson told the Daily Mail: 'It's a big eruption, but it is unlikely to be like last year.'
He was referring to the huge Eyjafjallajökull blast that brought parts of Europe to a virtual standstill in 2010.
He said the plume from the volcano, which last exploded in 2004, had been seen on radar screens as high as nine miles up, but he said the smoke was going straight up into the air.
University of Iceland geophysicist Pall Einarsson said: 'Grimsvotn is a very powerful volcano, so we're monitoring it closely, even if the last few eruptions have been harmless.'
He said ash was also coming from the volcano, but added: 'We do not expect this to be a big one as it's coming from the same crater as the last three eruptions, which were all small.'
A team of scientists from Iceland's capital Reykjavik flew to the area on Saturday to check on the situation.
Gudjon Arngrimsson, communications director for Icelandair, said: 'We do not expect the Grimsvotn eruption to affect air traffic to and from the country in any way.'
Air control authorities halted flights last year due to fears that the dust and ash from the Eyjafjallajökull volcano would get into engines and cause accidents after the cloud was blown into European air traffic lanes.
Mr Einarsson said: 'The ash in Eyjafjallajokull was persistent or unremitting and fine-grained.
'The ash in Grimsvotn is more coarse and not as likely to cause danger as it falls to the ground faster and doesn't stay as long in the air as in the Eyjafjallajokull eruption.'
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