Around 170,000 passengers were affected after Indonesia temporarily closed eight airports on Sunday as ash from Anak Krakatau spread across western parts of the country.
The disruption affected 1,558 flights, including 963 at Jakarta’s Soekarno-Hatta International Airport, with the airports ordered closed until midnight.
Authorities said no casualties had been reported, no evacuation order was issued and no tsunami warning was in effect.
Soekarno-Hatta was the first airport closed on Sunday morning after volcanic ash was detected in nearby airspace, while Jakarta’s Halim Perdanakusuma and six other airports were also shut.
The transport ministry said the disruption mainly affected flights to and from Singapore, alongside international routes involving Doha, Sydney and Kuala Lumpur.
Services at Bali’s I Gusti Ngurah Rai International Airport and Medan were also disrupted.
Transport Minister Dudy Purwagandhi urged airlines to accelerate refunds for canceled flights and provide timely information to passengers to prevent overcrowding.
Civil aviation officials warned that disruption could continue as airlines manage aircraft rotations, fleet availability and terminal capacity while restoring operations.
Anak Krakatau had shown activity since Friday, with continuous seismic activity, lava fountains and booming sounds reported before two eruptions early Sunday.
Indonesia’s Geological Agency said the volcano erupted for 30 seconds at 3:53 a.m. and again for 16 seconds roughly three hours later.
Officials said activity has intensified since July, with Sunday’s eruption the strongest during that period.
Satellite monitoring identified ash clouds reaching about 20,000 feet and 50,000 feet, spreading over parts of Jakarta, Banten, West Java, Lampung and Bengkulu, as well as nearby waters.
Authorities warned people to remain at least three kilometers from the active crater.
The health minister advised residents in affected areas to stay indoors and wear face masks because of respiratory, eye and skin risks.
Schools in ash-affected areas were authorized to temporarily shift to online learning, while reports of eye irritation prompted some school cancellations and fishermen to avoid trips at sea.