Indonesian authorities closed eight airports on Sunday, including the busiest one in Jakarta, after the eruption of the Anak Krakatoa volcano, located about 150 km away, grounding more than 170,000 passengers.

In addition to Jakarta's Soekarno-Hatta International Airport and Halim Airport, also located in the capital, Bandung and Radin International Airports, near Bandar Kampung in Sumatra, have been closed, as have four other smaller airports, the Ministry of Transport said in a statement.

"To date, 1,558 flights have been delayed at the eight affected airports, leaving 170,000 passengers stranded," the ministry announced in the evening. More than 900 of the affected flights were to or from Soekarno-Hatta International Airport, it specified.

Several airports in cities like Semarang and Surabaya have been prepared as "alternatives for landing", said Transport Minister Dudy Purwagandhi.

Flights at Jakarta airport were suspended at 1:30 a.m. Sunday morning and were extended several times. On Sunday evening, the suspension lasted until 11:59 p.m. local time (4:59 p.m. GMT).

Tests indicated "the dispersion of volcanic ash in the area of the Soekarno-Hatta International Airport" leading to "the closure of the airport", according to the Ministry of Transport.

The Anak Krakatoa volcano, which means "child of Krakatoa", erupted on Saturday, with a lava flow and detonations audible up to 700 kilometers away, the volcanology agency said in a statement, adding that two new eruptions had been recorded on Sunday.

The ash, which is dangerous for aircraft engines, spread into the airspace of several airports.

- "natural disaster" -

Henny Yensan, 44, who had hoped to return to her hometown of Bengkulu, Sumatra, but found herself stranded in Jakarta, noted that "everyone was disappointed." "No one got angry because, after all, it's due to a natural disaster," the businesswoman, who had to postpone her flight until Tuesday, told AFP.

The disruptions are also affecting Lombok airport as well as Bali airport, and sixteen domestic flights to and from the "island of the Gods" have been cancelled.

Samuel Guiberteau, an executive in a large multinational company, on a business trip to Lombok, was due to return to Jakarta on Sunday on a Pelita flight scheduled for 5:10 pm, which was cancelled.

"I had found another flight on Citilink but it was also cancelled," the 47-year-old Frenchman, who lives in the Indonesian capital and is going to spend the night in Lombok, told AFP by telephone.

Volcanic ash reached the city of Bandar Lampung, at the southern tip of Sumatra, covering parked cars and roadsides. "I fear this will severely affect the lungs and cause a lung infection," 25-year-old Andre Bayu Saputra told AFP.

Schools in Jakarta will be closed on Monday and classes will switch to remote learning, the city announced in a statement, without specifying the duration of this measure.

Located in the strait separating the islands of Java and Sumatra, the Anak Krakatoa volcano has experienced sporadic activity since its emergence at the beginning of the last century, within the caldera formed following the eruption of Krakatoa in 1883.

This disaster was one of the deadliest and most destructive in history, with an estimated death toll of 35,000.

Ships transiting the strait must "redouble their vigilance" in the face of potential navigational disruptions, the local port authority stressed.

Furthermore, boats are prohibited from entering an area with a radius of 3 kilometers around the volcano.

Volcano activity could intensify, as monitoring instruments continue to record tremors indicating lava movement inside the volcanic edifice, said Lana Saria, head of the geology agency.

"Seismic activity indicates the movement or release of volcanic fluids within the volcanic system. However, the timing, magnitude, and nature of the next eruption cannot be accurately predicted," she explained at a press conference.

There is currently no risk that the recent eruptions could trigger a tsunami, she added.

A tsunami in 2018, caused by the collapse of parts of Anak Krakatoa, killed 429 people and displaced thousands of residents.

Indonesia, a vast archipelago in Southeast Asia, is located on the Pacific Ring of Fire where the meeting of continental plates generates intense volcanic and seismic activity.