A father, two daughters, three sons and a cousin were found dead on Thursday morning in the Andhra Pradesh town of Mahavur, officials said.
They were found in the car in which they had gone to take a walk near the town’s road, which connects Mahavure to other villages.
Police said they had no reason to suspect foul play.
The bodies were taken to a nearby hospital, where they were pronounced dead on arrival.
A police officer said the dead had been taken to the local hospital to be formally identified.
Police are yet to identify the family members, or the three siblings.
Mahavur is just 60 kilometres (37 miles) from the capital, Bangalore, and is a popular tourist destination.
According to the official website, the town is home to around 100,000 people.
Police have not released the identities of the victims, but a Facebook page has been set up for their families.
The family members are believed to have left their home around 6am and were found on the road near the road’s boundary with the nearby town of Rajapattinam.
Police told The Hindu that they were not aware of any such incident before, but added that they are keeping a close watch on the area.
(With inputs from agencies)