Hours of heavy rain caused flooding in two districts -- Agam and Tanah Datar -- in West Sumatra province on Saturday evening, threatening thousands after it swept ash and large rocks down Mount Marapi.
"Until now our data shows that 34 people died: 16 in Agam and 18 in Tanah Datar. At least 18 others are injured. We are also still searching for 16 other people," West Sumatra disaster agency spokesman Ilham Wahab told AFP.
He said the search effort involved local rescuers, police, soldiers and volunteers.
Abdul Malik, head of Padang Search and Rescue Agency, told reporters three more people had died but they were yet to be confirmed by other authorities.
Agam and Tanah Datar were hit with flash floods and cold lava flow at around 10:30 pm (1530 GMT) on Saturday, according to the Basarnas search and rescue agency.
Cold lava, also known as lahar, is volcanic material such as ash, sand and pebbles carried down a volcano's slopes by rain.
About 370,000 people live in Tanah Datar, where several mosques and a public pool were damaged, with large rocks and logs scattered on the ground, according to an AFP journalist at the scene.
In Lembah Anai, a popular tourist spot with a waterfall in Tanah Datar, a road connecting the cities of Padang and Bukittinggi was severely damaged and access for cars was cut off.
Aerial images seen by AFP of Tanah Datar showed roads covered by mud, with roofs and a mosque's minarets jutting out of the sea of brown mud.
Ilham said Sunday that authorities were still receiving reports of missing people from relatives.
He said he could not give a figure for the number of people evacuated from the area because the search and rescue effort was still focused on the victims and the missing.
Trucks swept away
Two trucks had been swept away by the flooding and strong currents in a nearby river, the journalist said.
In Agam, which has a population of more than 500,000 people, dozens of homes and public facilities were damaged, the district's disaster agency chief Budi Perwira Negara told reporters.
He said 90 people had been evacuated to take shelter in a school.
Nine bodies, including those of a three-year-old and an eight-year-old, were identified on Sunday, Malik said in an earlier statement.
Authorities sent a team of rescuers and rubber boats to look for the missing victims and to transport people to shelters.
The local government set up evacuation centres and emergency posts in several areas of Agam and Tanah Datar.
Indonesia is prone to landslides and floods during the rainy season.
At least 26 people were found dead in March after landslides and floods hit West Sumatra.
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 natural defences against floods, slowing the rate at which water runs down hills and into rivers.
Marapi is the most active volcano on the archipelago's Sumatra island.
It erupted in December and spewed an ash tower about 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.
