Flights between Singapore and Jakarta in Indonesia have been suspended due to ash erupting from Mount Merapi in central Java.
Singapore Airlines, Japan Airlines, Malaysia Airlines, Lufthansa and Cathay Pacific are among carriers to have temporarily dropped services.
Airline officials say the ash is a safety threat and could damage aircraft.
Mount Merapi, one of the world’s most active volcanoes, began erupting two weeks ago, killing more than 130 people and forcing the evacuation of around 200,000 residents.
MAS operations director Azharuddin Osman said: “The volcanic ash presence in the airways surrounding Jakarta could cause severe damage to our aircraft and engines, which could impair the safety of our operations.”
Domestic flights have been unaffected.