Airlines are monitoring the possibility a new volcanic eruption in Iceland amid fears of another ash cloud disaster.

Already one transatlantic flight from London to San Francisco has been diverted around the area.

The Icelandic government’s weather service has issued a red alert to aviation after indications of a possible eruption under the country’s biggest glacier, the Vattnajokull.

The BBC reports that the Icelandic Met Office also warned that a small eruption had taken place under the Dyngjujokull ice cap.

Weather experts say seismic activity is continuing at the Bardarbunga volcano, some 20 miles away.

As a precaution airspace over the site has been closed and a Europe-wide alert has also been upgraded.

Eurocontrol, the European air safety regulator, is to produce a forecast of likely ash behaviour every six hours.

Airlines fear a repeat of chaotic scenes in April 2010 when Iceland’s Eyjafjallajokull volcano erupted and produced ash that severely disrupted air travel.

The Eyjafjallajokull eruption caused the largest closure of European airspace since World War Two.

The Virgin Atlantic airline has confirmed that it rerouted a flight from London to San Francisco away from the volcano as a precautionary measure.

In a statement the airline said: “Other flights continue to operate as normal.”

British Airways told the BBC: “We are keeping the situation under close observation but flights are continuing to operate normally for now.”

Britain’s Civil Aviation Authority (CAA) said there would be no impact on flights unless there was an actual eruption.

Icelandic police said: “The eruption is considered a minor event at this point,” police said in a statement.

“Because of pressure from the glacier cap, it is uncertain whether the eruption will stay sub-glacial or not.”