At least 17 people still missing after heavy rains washed mud and cold lava down the slopes of Mount Marapi.

A local disaster official told the AFP news agency that 17 other people remained missing after the downpour on Saturday night swept ash and large rocks down Mount Marapi, the most active volcano on Sumatra island.

Three people are missing in the Agam district and 14 in Tanah Datar, both the worst-hit areas of the flood and home to hundreds of thousands of people, Ilham Wahab, an official with the West Sumatra disaster mitigation agency, told AFP.

About 400 people, including police, soldiers and local rescue squads, have been deployed to search for the missing, using at least eight excavators and drones.

Marapi erupted in December, killing more than 20 people.

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

The rain turned roads into muddy rivers, swept vehicles away and damaged homes and other buildings.

Damage to the roads has hampered rescue efforts.

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.