Scores of rescue workers dug with spades and hoes in a search for survivors, said police Sgt. Satria Dinata. A backhoe was on the way to the scene.
The bus was hit late Friday as it traveled from Medan, the capital of North Sumatra province, to the town of Pasaman during a heavy rainstorm, Dinata said.
Rescuers had recovered 37 bodies, said Sgt. Ronnie Hamdani. Six other people were still buried, he said, adding 14 were injured.
Worried families gathered at the nearby Yarsi Hospital, looking for loved ones. Thirty-five bodies were brought to the morque, said nurse Genti Mar.
Medan is about 900 miles northwest of the capital, Jakarta.
Rampant deforestation and a lengthy rainy season cause dozens of landslides and flash floods each year in Indonesia.
Last month, a landslide in South Sulawesi killed 30 people, and 200 people died in November when a flash flood hit the Bukit Lawang resort in North Sumatra.
