"A complaint was lodged that a one-and-half-year-old girl was raped last night when she was sleeping with her mother on a footpath on Park Street," Deputy Commissioner of Police (South) Vishal Garg told PTI.
The infant was sent for medical examination, he said.
"We are on the lookout for the perpetrators and an investigation is already in progress," the DCP added.
The incident took place eight months after the rape of an Anglo-Indian woman set off a public outcry. The Anglo-Indian woman was raped in a car at Park Street in which she had taken a lift at night in February.
Chief Minister Mamata Banerjee was embroiled in a controversy after she described the incident as 'concocted' and aimed at tarnishing image of the state government.
The case was cracked by the Kolkata Police's crime wing then chief Damayanti Sen, with charge sheets filed against five persons. The prime accused in the case is still at large.