Authorities in Iceland have raised an aviation warning code to red after a small eruption began near the Bardarbunga volcano overnight.
The eruption took place early Friday morning in the Holuhraun lava field, north of Dyngjujkull glacier, Iceland's Meteorological Office said.
The Icelandic Air Traffic Control has closed down the air space from the earth up to 18,000 feet above the eruption site.
Scientists said the fissure eruption was one kilometre long. The warning was raised from orange to red – the highest possible – which indicates that an eruption is imminent or underway, with a risk of ash.
Iceland's largest volcanic system, which cuts a 190-km long and up to 25-km wide swathe across the North Atlantic island, has been hit by thousands of earthquakes over the last two weeks.
Video: Bardarbunga Volcano
A spokesperson for the UK Met Office confirmed no ash has been detected in the atmosphere yet.
In a statement, Iceland’s National Crisis Coordination Centre said: “The Icelandic Met Office has raised the aviation colour code over the eruption site to red and the Icelandic Air Traffic Control has closed down the airspace from the earth up to 18,000 feet.
“No volcanic ash has been detected with the radar system at the moment ... Seismic eruption tremor is low indicating effusive eruption without significant explosive activity.”
In 2010, Iceland's Eyjafjallajokul volcano erupted and sparked a week of international aviation chaos, with thousands of flights canceled. Aviation officials closed Europe's air space for five days, fearing that volcanic ash could harm jet engines.