Indonesian rescuers are searching for 7 people still missing four days after torrential rain hit North Sumatra province, causing flash flooding and landslides which killed 15 people, an official said on Tuesday.

Eleven people were killed in landslides in Karo district, Padang Lawas district and Tapanuli Selatan district, and another 4 died in flash floods in Deli Serdang district after the bad weather hit on Saturday, disaster agency spokesperson Abdul Muhari said.

About a hundred rescuers along with police and military were still searching for the seven missing people, but they had been hampered by persistent rain, Abdul said.

"It's still raining from the afternoon until the evening. This is the main obstacle while we try to locate the missing people," he said, adding the search would continue until Saturday.

The landslides and flash floods damaged houses, mosques, and rice fields. Road access was cut off to several villages, and excavators were being used in the search for victims and the missing.

The disaster agency warned people in North Sumatra province to anticipate potential floods in the coming weeks as more heavy rain is forecast, Abdul said.

Landslides are frequent in Indonesia, especially in the rainy season. The risk of landslides is often increased by deforestation and small-scale illegal mining operations in remote districts.