At least 17 people are now known to have died when a building collapsed in the southern Indian city of Chennai.
Some 22 survivors have so far been pulled from the rubble, and 40 others are feared trapped in the debris.
More than 70 workers were in the 11-storey building which was under construction when it toppled in heavy rain late on Saturday.
India has seen frequent building collapses, many blamed on lax safety and substandard materials.
At least six people, including construction company officials, have been arrested in connection with the collapse in Chennai (Madras), the capital of the southern state of Tamil Nadu.
"It appears they have not adhered to approved plans. The building appears to have serious structural defects," Tamil Nadu Chief Minister J Jayalalithaa said.
Hundreds of rescue workers, including personnel from India's National Disaster Response Force, are working with cutters, shovels and other equipment to search for survivors.
"Clearing the debris is a huge challenge. This would take almost two to three days and we are hopeful of saving many lives, going by our previous experiences in other places," senior police official SP Selvan told the NDTV news channel.
While the cause of the latest collapse is still under investigation, a lack of construction codes, leading to lax safety, is one reason for frequent collapses of buildings and other infrastructure projects in India.
There is also a high demand for housing, pushing up costs and forcing less affluent people to risk their lives in decrepit or badly constructed buildings.
Earlier on Saturday, a four-storey building came down in the capital Delhi, killing 10 people, including five children.
In January, at least 14 people died when a building under construction came crashing down in the western state of Goa.
At least 42 people died after a four-storey building collapsed in Mumbai last September.
Reproduced under licence from BBC News © 2014 BBC