Flash floods and mud slides in Indonesia's West Sumatra province killed at least 43 people over the weekend while a search for 15 missing people continued, authorities said on Monday.

Torrential rain on Saturday evening triggered flash floods, landslides, and cold lava flow - a mud-like mixture of volcanic ash, rock debris and water - in three districts in West Sumatra province, Abdul Malik, chief of the provincial rescue team, told Reuters.

The cold lava flow, known in Indonesia as a lahar, came from Mount Marapi, one of Sumatra's most active volcanoes.

In December, more than 20 people were killed after Marapi erupted. A series of eruptions has followed since.

"The heavy rain swept materials such as ash and large rocks from the Marapi volcano," said Abdul Malik, who later added in a statement that 43 people had died and 15 remained missing.

"Cold lava flow and flash floods have always been threats to us recently. But the problem is, it always happens late at night until dawn," he said.

Abdul said around 400 personnel, including rescuers, police, and military, were deployed to search for the missing people on Monday, helped by at least eight excavators and drones.

The national disaster and management agency BNPB said in a statement almost 200 houses were damaged and 72 hectares (178 acres) of lands, including rice fields, were affected. At least 159 people from Agam district were evacuated to nearby schools.

Footage shared by BNPB showed roads and rice fields covered by mud. Video also showed the wreckage of damaged homes and buildings, while the floods brought logs and large rocks into settlements.

Eko Widodo, a 43-year-old survivor, said: "The flooding was sudden and the river became blocked which resulted in the flow of water everywhere and it was out of control."