Police said the occupants of the car were proceeding to Thandigudi, near Kodaikanal, where their relative was studying in a college, when the mishap occurred early this morning.
The victims were identified as Venkatachalam (37), his wife Geetha (35), Geetha's sister Banu (42), Venkatachalam's son Balaji (11), the driver, Mohan, and Shanthi (41), relative of Venkatachalam.
A case has been registered, police said.