Rescuers have recovered more bodies after monsoon rains triggered flash floods on Indonesia’s Sumatra Island, bringing down torrents of cold lava and mud, leaving 43 people dead and another 15 missing.

The heavy rains, along with a landslide of mud and cold lava from Mount Marapi, caused a river to breach its banks.

The deluge tore through mountainside villages along four districts in West Sumatra province just before midnight Saturday.

The floods swept away people and submerged hundreds of houses and buildings, while forcing more than 3,100 people to flee to temporary government shelters in Agam and Tanah Datar districts, said National Disaster Management Agency spokesperson Abdul Muhari.

Cold lava, also known as lahar, is a mixture of volcanic material and pebbles that flow down a volcano’s slopes in the rain.

Rescuers on Monday recovered more bodies, mostly from villages that were worst hit in Agam and Tanah Datar districts, bringing the death toll to 43, Mr Muhari said in a statement.

At least 19 people were injured in the flash floods and rescuers are searching for 15 villagers reported missing, he said.

Authorities struggled to get tractors and other heavy equipment to the area over washed-out roads after flash floods brought mud and rocks on to the hilly hamlets, said Abdul Malik, who heads the search and rescue office in Padang, the provincial capital.

Hundreds of police, soldiers and residents dug through the debris with their bare hands, shovels and hoes as rain, damaged roads and thick mud and debris hampered relief efforts.

“The devastated area is so vast and complicated, we badly need more excavators and mud pumps,” Mr Malik said.

Flash floods on Saturday night also caused main roads around the Anai Valley Waterfall area in Tanah Datar district to be blocked by mud, cutting off access to other cities, Padang Panjang police chief Kartyana Putra said on Sunday.

Videos released by the National Search and Rescue Agency showed roads that were transformed into murky brown rivers and villages covered by thick mud, rocks, and uprooted trees.

Heavy rains cause frequent landslides and flash floods in Indonesia, an archipelago nation of more than 17,000 islands where millions of people live in mountainous areas or near floodplains.

The disaster came just two months after heavy rains triggered flash floods and a landslide in West Sumatra, killing at least 26 people and leaving 11 others missing.

A surprise eruption of Mount Marapi late last year killed 23 climbers.

Marapi is known for sudden eruptions that are difficult to predict because the source is shallow and near the peak, and its eruptions are not caused by a deep movement of magma, which sets off tremors that register on seismic monitors, according to Indonesia’s Centre for Volcanology and Geological Disaster Mitigation.

Marapi has been active since an eruption in January 2024 that caused no casualties.

It is among more than 120 active volcanoes in Indonesia.

The country is prone to seismic upheaval because of its location on the Pacific Ring of Fire, an arc of volcanoes and fault lines encircling the Pacific Basin.