Police in southern India have detained two construction company directors as rescuers using gas cutters and shovels searched for workers buried in the rubble of a building that collapsed during monsoon rains.
It was one of two weekend building collapses that killed at least 22 people.
The unfinished 11-storey apartment building collapsed late on Saturday while heavy rains and lightning were pounding the outskirts of Chennai, the capital of Tamil Nadu.
Police said 28 construction workers had been pulled out and the search was continuing for more than a dozen others.
Four of the workers died on the spot and another five succumbed to injuries in hospital.
Watch: Dozens killed and trapped after building collapsed in southern India
Feeble voices were being heard from those trapped in the debris, said T.S. Sridhar, the disaster management agency commissioner. Rescuers used gas cutters, iron rods and shovels after cranes lifted concrete blocks to get to the survivors.
Nearly 90 contract workers were believed to have been in the basement to collect their weekly wages when the building collapsed, Sridhar said, adding that the exact number of those trapped was unknown. The building was one of two towers being built in the area, he said.
"Removing debris is a major challenge. It may take two to three days to clear the rubble," said S.P. Selvam, who is heading the rescue operation.
Police said two directors of the construction company, Prime Sristi, had been detained for questioning as authorities began investigating the collapse.
Balaguru, one of the builders, said the structure might have collapsed when it was hit by lightning.
Earlier on Saturday, a four-storey, 50-year-old structure toppled in a poor area of New Delhi.
Eleven people died, including five children, and one survivor was being treated in hospital.
Most homes in that area were built without permission and using substandard materials.
The Press Trust of India 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-storey building being constructed illegally in Mumbai caved in. It was the worst building collapse in the country in decades.