The aviation industry has been warned about the possibility of flight disruptions caused by activity at Iceland's largest volcano system.

Intense seismic tremors have been recorded at Iceland's Bardarbunga volcano for the past three days, although there are no signs yet of an eruption.

The country's weather office has raised the risk level to the aviation industry to orange - the fourth level on a five-level scale.

It said in a statement that the strongest earthquake in the region since 1996 was recorded early on Monday.

It said "As evidence of magma movement shallower than 10km implies increased potential of a volcanic eruption, the Bardarbunga aviation colour code has been changed to orange."

"Presently there are no signs of eruption, but it cannot be excluded that the current activity will result in an explosive sub-glacial eruption, leading to an outburst flood and ash emission. The situation is monitored closely," it added.

Image: Google Earth

The Icelandic Met Office says that over the last seven years seismic activity has been gradually increasing at the site. And that while this activity dropped down in May 2011, it has started to gradually increase again.

In 2010 an ash cloud caused by the eruption of Iceland's Eyjafjallajokull volcano shut down much of Europe's airspace for six days. More than 10 million people were affected by the event.

Bardarbunga is Iceland's largest volcanic system. It is located under the ice cap of the Vatnajokull glacier, in the country's south-west.

Seismologist Martin Hensch said the risk of any disruptive ash cloud similar to the one in 2010 would depend on several factors, including how high any ash coming from the volcano would be thrown.

He added that the biggest risk in Iceland would be caused by flood waves from an eruption beneath the glacier.