STOCKHOLM (Reuters) - A new fissure eruption in an ice-free area of Iceland's Bardarbunga volcano system prompted authorities to raise their warning level for the risk of ash to aviation to the highest level of red on Sunday.

Iceland's largest volcanic system, which cuts a 190 km long and up to 25 km wide (118 miles by 15.5 miles) swathe across the North Atlantic island, has been hit by thousands of earthquakes over the last two weeks and scientists have been on high alert.

In 2010, an ash cloud from the Eyjafjallajokull volcano, in a different region of Iceland, closed much of Europe's air space for six days.

"A small eruption started at 0600 this morning," the Department of Civil Protection and Emergency Management said in a statement.

"The Icelandic Met Office has raised the aviation color code to red for Bardarbunga/Holuhraun."

Red is the highest level on a five-color scale and indicates that an eruption is imminent or under way, with a risk of spewing ash.

On Friday, a 600 meter-long fissure 5 km north of Dyngjujokull glacier in the north Vatnajokull glacier erupted but no ash was detected at the time.

That eruption only lasted for a few hours.

"This is a little bit larger fissure eruption than on Friday," Armann Hoskuldsson, a geologist at the University of Iceland who is working in the area, told Reuters.

"There is more lava and more rifts in the ice cap. The rifts are approximately 1 km further to the north than after the fissure eruption on Friday."


(Reporting by Robert Robertsson; Editing by Hugh Lawson)