All the six, including two women, died on the spot in the accident which occurred near Kayathaaru, about 140 km from here, when the tourists were on their way to Kanyakumari.
Quoting preliminary investigation, police said the driver dozed off and lost control when the van was speeding, resulting in the accident.
The tourists had arrived here by train and left for Kanyakumari by van late last evening.
Police, on being alerted about the accident by drivers of vehicles which passed by the spot, rushed and rescued five injured persons with the help of employees of a nearby toll plaza.
The deceased were identified as Rekha, Vindhya, Rameskumar, Kanayalal, Deekam and Lalchand.