The incident happened early morning under Barari police station when the Chhath devotees were trying to cross the road, Senior Superitendent of Police (SSP)Vivek Kumar Singh said.
The truck has been seized and the driver has been arrested. The critically injured devotee has been admitted at Jawaharlal Nehru Medical College and Hospital for treatment, SSP added.
Irate locals tried to set the truck on fire after the mishap, but Rapid Action Force (RAF) rushed to the spot and foiled the attempt.