Indonesia’s Bali airport saw dozens of flights canceled because of a volcanic eruption nearby, stranding holidaymakers and threatening the area’s key tourism industry.

Singapore Airlines, Jetstar Airways, AirAsia X, Batik Air and Wings Air were among airlines that halted flights, citing the volcanic activity, taking the cancellations to at least 30, according to data on Bali’s international airport website on Wednesday.

The disruptions followed Tuesday’s eruption of the Mount Lewotobi Laki-Laki volcano in the east of Indonesia’s Flores island. Authorities raised the volcano’s disaster alert to the highest level of four after the eruption sent an ash column of over 10 kilometers into the sky, the country’s disaster management agency said in a statement.

Although the airport at Denpasar, the main gateway facility to the tourist hotspot of Bali, remained open and some carriers including PT Garuda Indonesia were still checking passengers in, the Volcano Observatory Notice for Aviation said gray volcanic ash of a medium intensity was observed moving toward the north. Flight information data from the airport showed several arrival and departure services were still scheduled in the afternoon and evening.

Seismic monitoring devices are still detecting tremors, indicating ongoing volcanic activity, the disaster management agency said.