The 12-story apartment structure the workers were building collapsed late Saturday while heavy rains and lightning were pounding the outskirts of Chennai, the capital of southern Tamil Nadu state. Police said 26 construction workers had been pulled out so far and the search was continuing for more than a dozen others.
Four of the workers died on the spot and another four succumbed to injuries later in a hospital, said police officer George Fernandes.
Twelve injured workers have been hospitalised, while six others were allowed to go home after medical attention on Saturday night, Fernandes said.
Authorities are investigating the cause of the collapse.
Nearly 300 policemen and fire service workers worked overnight, looking for survivors in the debris. They used gas cutters, iron rods and shovels to reach those trapped in the rubble.
Earlier Saturday, a four-story, 50-year-old structure toppled in an area of New Delhi inhabited by the poor. Eleven people died and one survivor was being treated in a hospital, said fire service officer Praveer Haldiar.
Most homes in that part of the capital were built without permission and using substandard materials, police officer Madhur Verma said.
The Press Trust of India news agency said the New Delhi collapse was triggered by construction work on an adjacent plot.
Building collapses are common in India, where high demand for housing and lax regulations have encouraged some builders to cut corners, use substandard materials or add unauthorised extra floors.
In April last year, 74 people were killed when an eight-story building being constructed illegally in the Mumbai suburb of Thane in western Maharashtra state caved in. It was the worst building collapse in the country in decades.