The latest information indicated the boat was still near Anak Krakatau at around 18:13 on Monday, Amrad said. "So far, the search has yielded no results."

Indonesia's National Search and Rescue Agency, Basarnas, deployed four teams to search waters around Anak Krakatau, Rakata Island and Panjang Island. All eight people remained missing as of Wednesday morning.

Anak Krakatau has continued to erupt intermittently, with authorities maintaining a three-kilometre exclusion zone around its active crater.

German traveller Ana said her flight to Lombok had been cancelled and passengers were struggling to get clear information. "It's a little bit difficult for us because nobody can tell us anything about the flights and where we can get our money back and what the next step is," she said.

Passenger Ronald Tampubolon said his flight had been delayed from 11:00 to 14:00, while another traveller, Maurin, said long queues made both refunds and rescheduling difficult.

Reports said hundreds of flights and around 22,800 passengers were affected at Soekarno-Hatta. A further 31 Jakarta-bound flights were cancelled at airports across Malaysia.

Anak Krakatau, located in the Sunda Strait between Java and Sumatra, erupted repeatedly on Saturday. Indonesia's meteorological agency reported ash plumes reaching up to 6,000 metres on the Java side and as high as 15,000 metres on the Sumatra side and over parts of Banten province.

Around 85 families, or about 350 people , were transported to a temporary shelter at the Municipal Hall of San Juan Alotenango.

Volunteer firefighter Leandro Amado said the operation was carried out at the request of residents.

"This evacuation was carried out for people who voluntarily asked to be assisted. We deployed more than 25 personnel and 11 pickup trucks, four-by-four, to be able to enter areas of difficult access," Amado said.

Authorities continued monitoring the volcano due to emissions of ash, gases, volcanic material and the risk of hot flows descending its slopes.

The National Coordinator for Disaster Reduction (Conred) ordered the preventive measures as volcanic activity increased.

Fuego volcano, one of Central America's most active volcanoes, remains under continuous monitoring by the National Institute of Seismology, Volcanology, Meteorology, and Hydrology (Insivumeh) and emergency response agencies.