Seismic activity at Iceland's Bardarbunga volcano eased slightly overnight after a series of large quakes and there were still no signs of an eruption, the country's Met Office said early on Monday.

Authorities have been on alert since increased movement at Iceland's largest volcano system this month triggered memories of the eruption of the Eyjafjallajokull volcano in 2010 that shut down much of Europe's airspace for six days.

Bardarbunga, located under the ice cap of a glacier, was hit by a magnitude 5 quake late on Sunday, one of several large quakes during the day.

"There have been no large events at the Bardarbunga volcano since yesterday (Sunday) and there is no sign of volcanic tremors," Gunnar Gudmundsson, geophysicist at the Icelandic Met Office said.

"There is still high activity, but maybe not so intense as yesterday."

On Sunday, Iceland lowered its warning code for possible volcanic disruption to the aviation industry to orange from red, the highest level on the country's five-point alert system, after concluding that seismic activity had not led to a volcanic eruption under the glacier.

Red alert indicates an eruption is imminent or underway with a significant emission of ash likely.

There have been thousands of smaller quakes over the past week at Bardarbunga. Areas around the volcano, in the center of the North Atlantic island nation, have been evacuated.

Bardarbunga is in a different range to Eyjafjallajokull.