The worst-hit region was the west of Indonesia's main island of Java, where torrential downpours in Garut saw floodwaters quickly rise to 2 metres, national disaster agency spokesman Sutopo Purwo Nugroho said in a statement.
"The official report (from Garut)... Is that 16 people were killed and eight others are still missing," he said.
Among the dead from the fast-rising floods were an eight-month-old toddler and four other children under the age of ten, Sutopo added, citing a casualty report from the local disaster agency in Garut.
Elsewhere in West Java, the death toll from a landslide in Sumedang regency rose to three, with one other person still believed missing beneath an avalanche of mud and rock.
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The landslide left two others injured and destroyed a mosque, Sutopo added.
Landslides and flooding are common in Indonesia, a vast tropical archipelago prone to natural disasters and torrential downpours.
The country's disaster agency has warned people to be alert for disasters this wet season as a La Nina weather phenomenon threatens unseasonably heavy rain.