The accident took place at Balsrigitim area near Baghmara, the district headquarters of South Garo Hills, about 350 km from state capital Shillong.
"Four people died on the spot and three others succumbed to their injuries at a hospital and 32 were injured," district police chief Lakardor Syiem told IANS over phone.
Of the injured, three were in a critical condition and have been rushed to the Tura government hospital.
The bus driver has been detained and investigation is on to ascertain the cause of the accident.
A preliminary probe revealed that the driver lost control of the vehicle.
The bus was ferrying passengers to Baghmara from Tura, the district headquarters of West Garo Hills, he said.