A plume of volcanic ash has disrupted a plethora of European flights, with delays expected to last as long as two days.

A volcano at southern Iceland glacier Eyjafjallajokull, is emitting volcanic ash into the atmosphere, making it dangerous for aircraft to fly through.

Qantas has cancelled all flights to London Heathrow and Frankfurt, with customers travelling to Singapore offered new flights.

A decision on journeys to Bangkok and Hong Kong is yet to be made, with Qantas currently assessing services to both ports.

Services from London Heathrow to Australia via Singapore and Bangkok have also been cancelled.

Qantas is giving passengers with valid tickets from April 15 to April 18 the option to re-route travel via the most direct routing using Qantas, return to the origin port via the most direct routing using Qantas, retain the value of the ticket in credit for future travel or defer travel.

British Airways is advising customers on its website that all British Airways flights operating to and from London Heathrow and Gatwick airports will be cancelled until at least 7pm local time on Friday.

It said customers booked to travel on a cancelled flight were claim a full refund.

Both airlines have advised customers to monitor their websites for further updates.