A 38-year-old German woman tourist alleged that she was sexually assaulted at Mamallapuram beach.
In her complaint to the police, the victim alleged that she was forcibly taken away by some men, a district police official said.
The official said the incident took place when the victim was taking a stroll along the sea shore in the tourist town of Mamallapuram.
The woman was taken to a hospital for medical examination and the probe is on, he said.
Several persons are being questioned and some of them have been detained, he added.