Indonesia
AFP

Rescuers recovered more bodies on Tuesday after weekend flash floods and cold lava flow on Indonesia's Sumatra island killed at least 50 people and left another 27 missing, the country's disaster agency said.

Hours of heavy rain caused large volcanic rocks to roll down one of Indonesia's most active volcanos into six districts on Sumatra island Saturday evening while flooding inundated roads, homes and mosques.

Workers cleaned up damaged buildings after the deluge while rescuers deployed a thermal drone to help the search, using excavators and their bare hands to try to find survivors in the rivers and rubble.

"For the emergency response, heavy equipment has moved to clean up the disaster areas. And after this, we will go to shelters to ensure affected communities are served well," national disaster mitigation agency (BNPB) chief Suharyanto told reporters Tuesday.

The official, who goes by one name, raised the death toll from 44 to 50 and said 27 people were still missing and 37 had been injured. More than 3,300 people have also evacuated from the affected areas.

Authorities warned the death toll could rise further as the search for the dozens missing continued.

The search was urgent as rescuers only had a "golden time" of six days to find survivors, Suharyanto said.

Residents described the thundering noise they witnessed late Saturday when large volcanic rocks bowled down from Marapi and their fear as terrifying rains inundated their neighbourhoods.

"Now, [we are] very traumatised. Me and my family are afraid to stay there again. I feel like renting somewhere else," said Refki Amelia, a 39-year-old mother-of-three in Agam who survived but lost her mother and niece.

Dozens of houses were swept away and rescuers said many of the victims were found in or around nearby rivers.

Workers rushed to clear and repair a damaged bridge to ease access to the area.

To aid the rescue effort, authorities said they would deploy weather modification technology that will start to work from Wednesday.

"Efforts were made so the these rain clouds would not fall at the location of the disaster," meteorological agency chief Dwikorita Karnawati told reporters.

Aid deliveries were being carried out using air and land routes, some of which required emergency bridges, after the flooding and cold lava flow cut off some road access in the worst-hit areas, Suharyanto said.

BNPB spokesman Abdul Muhari on Monday said 71 houses were completely swept away and 125 were moderately damaged by the flooding and cold lava flow.

Cold lava, also known as lahar, is volcanic material such as ash, sand and pebbles carried down a volcano's slopes by rain.

Indonesia is prone to landslides and floods during the rainy season.

In 2022, about 24,000 people were evacuated and two children were killed in floods on Sumatra island, with environmental campaigners blaming deforestation caused by logging for worsening the disaster.

Trees act as a natural defence against floods, slowing the rate at which water runs down hills and into rivers.

Marapi is one of Indonesia's most active volcanos.

In December, it erupted and spewed an ash tower 3,000 metres (9,800 feet) into the sky, taller than the volcano itself.

At least 24 climbers, most of them university students, died in the eruption.