Indonesia shut down its primary international airport and seven others on Sunday, stranding roughly 170,000 passengers and grounding hundreds of flights after Mount Anak Krakatau ejected volcanic ash and lava from a distance exceeding 150km.
Classes in schools across Jakarta were moved online on Monday, according to a city statement, which did not indicate how long the measure would remain in effect.
Shipping operations have also faced disruption.
The airport authority announced via Instagram that the suspension had been prolonged until 8:59am local time on Monday "due to increased eruptive activity at Mount Anak Krakatau."
The geology agency reported that Anak Krakatau erupted on Saturday, sending up a fountain of lava and producing sounds that carried for several hundred kilometres.
The country's volcanology agency recorded two additional eruptions on Sunday.
According to the ministry, ash from the volcano was identified in the airspace around Soekarno-Hatta international airport, leading authorities to halt operations.
Operations were also suspended at seven other airports, among them the Husein Sastranegara airport in Bandung and Radin Inten II airport near Bandar Lampung on Sumatra, the ministry reported.
"To date, 1,558 flights have been delayed at the eight affected airports, with 170,000 passengers stranded," the ministry said in a Sunday statement.
It added that more than 900 of the affected flights operated to and from Soekarno-Hatta.
Transportation minister Dudy Purwagandhi noted that airports in cities including Semarang and Surabaya had been readied as alternative landing sites.
The disruption forced some passengers to seek alternative travel arrangements.
Henny Yensan, 44, who had planned to travel to her hometown with her mother, said "everybody was disappointed."
"No one flew into a rage because, after all, this is due to natural disaster," the businesswoman, who had to reschedule her flight to Tuesday, told AFP.
Volcanic ash reached Bandar Lampung at the southern tip of Sumatra, covering parked cars and roadsides.
Anak Krakatau, meaning Child of Krakatau, lies in a strait between the islands of Java and Sumatra.
Ships traversing the strait were instructed to exercise heightened caution due to potential navigation hazards from volcanic activities.
Local port authorities stated in a notice that vessels are barred from entering an exclusion zone with a 3km radius around the volcano.
The volcano has shown intermittent activity since rising from the sea early in the previous century, emerging within the caldera created by the 1883 eruption of Mount Krakatau.
That event ranks among the deadliest and most destructive in recorded history, with an estimated 35,000 fatalities.
Geology agency head Lana Saria cautioned against approaching Anak Krakatau, noting that materials expelled by the volcano could pose risks to those within the exclusion zone.
She stated that the recent eruptions do not carry the potential to generate a tsunami.
A collapse of portions of Anak Krakatau in 2018 caused a tsunami that killed 429 people and displaced thousands.
Indonesia, an archipelago nation in South-east Asia, lies along the Pacific Ring of Fire, an area where tectonic plate collisions produce significant volcanic and seismic activity.
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