The mishap took place near Dedhiya village when a car carrying 14 members of a family on a pilgrimage collided with a water tanker about 120km from here.
"Four persons were killed and ten others sustained critical injuries when their driver rammed the car into a water tanker near Dedhiya village," Sub-Inspector Harpalsinh Chauhan of Vejalpur Police Station said.
The deceased persons were identified as Bhavika Yadav, her sister Renuka, their mother Santosh (43), and Bhavika's grandmother Narayani (65), said Chauhan.
The driver could not see the tanker which was watering trees planted near the divider on the highway and crashed into it, Chauhan said, adding four car occupants died on the spot.
Police have sent the bodies for post-mortem and registered a case of rash driving, he said.