It was one of two weekend building collapses that killed at least 22 people.
Nearly 90 contract workers were believed to have been in the basement of the 11-storey structure to collect their wages when it collapsed on the outskirts of Chennai, the capital of Tamil Nadu state. Police said 31 had been pulled out so far, four died on the spot and another seven succumbed to injuries in hospital.
Officials used gas cutters, iron rods and shovels after cranes lifted concrete blocks to get to the survivors.
Police said two directors, two engineers and one supervisor of the construction company, Prime Sristi, were detained for questioning as authorities began investigating the collapse.
Balaguru, one of the builders, said the structure collapsed possibly due to the impact of lightning.
Earlier, 11 people died and one survivor was being treated in hospital after a four-storey, 50-year-old structure toppled in an area of New Delhi inhabited by the poor. Most homes in that part of the capital were built without permission and using substandard materials, police officer Madhur Verma said.
Building collapses are common in India, where lax regulations have encouraged some builders to cut corners.
In April last year, 74 people were killed when an eight-storey building being constructed illegally in the Mumbai suburb of Thane in western Maharashtra state caved in.