Several airlines have temporarily suspended flights between Singapore and Jakarta because of volcanic ash spewing from Mount Merapi in central Java.
Among those affected were Singapore Airlines, Japan Airlines, Malaysia Airlines, Lufthansa and Cathay Pacific.
Merapi, one of the world's most active volcanoes, began erupting two weeks ago and has killed more than 130 people.
Airline officials say the ash is a safety threat and could damage aircraft.
Domestic flights have been unaffected.