Iceland has closed its the main airport and cancelled domestic flights after the country's most active volcano, Grimsvotn, began erupting.
A plume of smoke has risen 20km (12 miles) into the sky from the volcano.
But Iceland's Meteorological Office says the eruption should not cause widespread disruption to air traffic.
Last year, ash clouds from another Icelandic volcano, Eyjafjallajokul, led to the closure of a large section of European airspace.
Governments feared that ash particles could cause aircraft engines to fail, and the closure caused chaos to air travellers.
Different ash
Hjordis Gudmundsdottir, a spokeswoman for the Isavia civil aviation authority - which has imposed a flight ban of 120 nautical miles (222 km) around Grimsvotn - said: "We have closed the area until we know better what effect the ash will have."
Keflavik airport, the country's main hub, will remain shut for the rest of the day, the authority said.
But officials say the eruption is unlikey to have the same impact as last year's.
Pall Einarsson, a geophysicist at the University of Iceland, said the 2010 eruption was a rare event.
"The ash in Eyjafjallajokull was persistent or unremitting and fine-grained," he said.
"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."
Icelandair pilot Thor Kristinsson told the BBC he had flown near the volcano on Saturday.
"We were able to finish our flight but we did see the ash plume rise fast. We were at 38,000 feet ... and the ash was at least at 40,000 feet at that time.
"It looks at least as bad as the one last year and it looks like it could get worse. It's as big, if not bigger than the last ash cloud."
Grimsvotn lies under the the largest glacier in Europe, Vatnajokull in south-east Iceland.
Reuters news agency says that when it last erupted in 2004, transatlantic flights had to be re-routed south of Iceland, but no airports were closed.
Last year's outpouring of ash from Eyjafjallajokull led to the largest closure of European airspace since World War II.
About 10 million travellers were affected and some questioned whether the shutdown was an over-reaction.
However, a scientific study published last month said the safety concerns had been well founded.
Researchers from the University of Copenhagen and the University of Iceland said ash particles from the early part of the Eyjafjallajokull eruption were especially abrasive, posing a possible threat to aircraft engines.
More in depth on the Iceland volcano eruption:
http://earthquake-report.com/2011/05/21 ... n-volcano/
