A volcanic eruption has occurred near Iceland's Dyngjujokull glacier, prompting authorities to raise the warning code for aviation to red, the highest level, but no volcanic ash has been detected, Iceland's authorities said.

There has been heightened seismic activity in the area for about a week.

"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 18000 feet," Iceland's National Crisis Coordination Centre said.

"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."

Ash from the eruption of Iceland's Eyjafjallajokull volcano in 2010 shut down much of Europe's airspace for six days.

The red code indicates that an eruption is imminent or underway with a significant emission of ash likely.