Police said armed groups from neighboring Arunachal Pradesh attacked Chauldhuwa, a border village in a forest area in Assam's Sonitpur district, leaving at least 10 dead and another eight injured.
The Times of India said tensions over a boundary dispute have been simmering for decades.
"People from Arunachal attacked a village in our state. We are sending additional forces there," a Sonitpur police official was quoted as saying.
The Calcutta Telegraph quoted police as saying the attackers fired on a group of people from the Assam side as they tried to stop the attackers from encroaching on their land.