Police said the mishap took place on National Highway 37 in Janji town around 4.30 am when the tanker, on way from Jorhat to Digboi, hit a truck coming from the opposite direction.
The driver of the truck, Krishna Kalita, died at the spot. Four other persons sustained serious injuries in the accident.
The injured have been shifted to Guwahati for furrther treatment.
Meanwhile, in another incident late last night, a police constable was seriously injured after being hit by a night service bus in Jorhat city.
The accident took place when the bus, on its way from Jorhat to Guwahati, hit constable Mintu Saikia outside the Polibor police station. The driver of the bus was arrested.
Saikia is undergoing treatment at the Jorhat Medical College.