The jeep was taking back a marriage party from Kharva village in Uttarkashi district to Lambgaon Abki village in Tehri district late last night, he added.
The driver lost control near Chulikhet and the vehicle fell into the river Jalkur village killing five persons on the spot and leaving as many injured.
One person succumbed to injuries while undergoing treatment at Uttarkashi district hospital, District Magistrate Ashish Chauhan said.
The condition of two of the injured was said to be serious and they were referred to a higher centre, he said.
Operations continued late in the night to recover the bodies and rescue the injured, he added.