Two unusually large earthquakes hit one of Iceland's biggest volcanoes early today, raising concerns of a possible eruption, the Icelandic Met Office said.

The Katla volcano has not erupted properly since 1918 and scientists say it is overdue to do so, although an eruption could still be decades away.

"It is quite a dynamic situation now, in the next hours and days following this, but as we speak at the moment we do not see any signs that there is an imminent hazardous unrest about to happen," Matthew Roberts, a natural hazards scientist at the Icelandic Met Office, said.

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

Katla, in southern Iceland, was rocked by quakes of magnitude 4.5 and 4.6 overnight. The volcano sustained similar movements in 2011.

The volcano is covered by an ice cap, which should, in the event of an eruption, typically contain the lava for around 60 to 90 minutes, giving time to alert the population and international air traffic, Roberts said.