A group of extremists came in two motorcycles and hurled two grenades in the remote Molandubi Bazar of Kazigaon sub-division around 2 PM, they said.
The ultras then opened indiscriminate fire on the people killing a businessman, Mokleb Ali, on the spot. Several others were seriously injured in the firing and grenade blast.
The exact number of injured was not immediately known as some were taken to hospitals in neighbouring Dhubri district and others to the adjacent areas in West Bengal, police said, adding senior police officers rushed to the spot.