At least 38 people were killed in flash floods in a remote region of Indonesia's North Sumatra province Tuesday, a spokesman for the provincial government said.

The early morning flood hit the coastal district of Mandailing Natal 275 kilometres (170 miles) southwest of the provincial capital Medan, Edy Syopian told AFP.

"Our latest information from the local district head is that 38 bodies have been found so far," he said.

"Our main priority is to rescue the survivors. The flash floods hit six villages with about 2,200 residents," he said.

Powerful waters unleashed after the Sulang Aling river overflowed uprooted trees and smashed through houses in the district, which has largely been cut off from outside contact, Syopian said.

"The rescue process is difficult because the two bridges... to the villages collapsed," he said.

"The other way to reach the affected area is by sea using speed boats, but strong weather... is making that difficult."

Health ministry crisis centre head Rustam Pakaya said a rescue team had been sent to the flood-hit area but had been delayed by the tough conditions.

"The rescue team is on the way. It's hard to reach the area because the roads are muddy," Pakaya said.

"The rescue team set off around midday but we estimated it would take them eight or nine hours to get there, so it will be a few hours more."

He said the floodwaters, which hit at around 2:00 am (1900 GMT Monday) reached around two metres (six feet) in height and displaced around 2,000 people.

Pakaya gave a figure of 12 people dead and 25 missing. North Sumatra government spokesman Syopian said he was unsure if the higher total of 38 included those listed as missing by the health ministry.

North Sumatra governor Syamsul Arifin was quoted by state news agency Antara as saying 50 tonnes of rice had been taken from government reserves to feed victims of the floods.

"We have instructed the local social services office to provide food and assistance, including blankets and tents, while for the time being the health office is providing medicine," Arifin said.

Floods and landslides are common in Indonesia, which is densely populated and prone to frequent heavy rains.

Activists have warned that logging and a failure to reforest denuded land in the world's fourth-most populous country are often to blame.