The trio, who had set off from Kerala on an autorickshaw for a tour of the North East, were on their way to Siliguri en route to Sikkim when their vehicle turned turtle at Ghakuchi, police said.
The tourists -- Andrew John, Stephen Doneur and Sarit Jay Patel -- were injured in the incident with John being in a critical condition while the two others received minor injuries.
The tourists were admitted to the Rangiya Civil Hospital but were later referred to the Guwahati Medical College Hospital.