Emergency workers from the National Disaster Response Force (NDRF) have pulled 20 survivors -- including two boys aged four and seven -- from the rubble of the building in Bhiwandi, near Mumbai.
An NDRF spokesman told reporters that recovery teams, aided by sniffer dogs, also retrieved 20 bodies buried under layers of brick and concrete when the three-storey block came crashing down before dawn on Monday.
NDRF director general Satya Narayan Pradhan tweeted that he expected the toll to increase, with "more (bodies) likely under debris".
The cause of the accident was not immediately clear, but building collapses are common during India's June-September monsoon season, with old and rickety structures buckling after days of non-stop rain.
So far, 25 injured persons have been admitted to hospitals while around 20 people were rescued by locals immediately after the building collapsed.
"There was a power loom at the ground floor of the building where some workers are believed to be asleep when the building caved in. As per details given by local people, 20 to 25 people are still trapped inside the debris," said Milind Palsule, public relation officer of the local civic body.
Bhiwandi, a textile hub with the largest power looms in india, has off-late turned into a logistics hub with several e-commerce companies having their warehouses there to cater to Mumbai's consumer demand.
The 43-year-old building had 40 apartments and nearly 150 persons were residing there, according to civic officials.
National Disaster Response Force, which is undertaking rescue and relief operations along with local administration, is now working in shifts.
Indian Prime Minister Narendra Modi and Home Minister Amit Shah had expressed their condolence on the unfortunate incident.
Building collapses in india happen more often in the monsoon season during the June-September period with torrential rains.
Last month, over a dozen people died after a building collapsed in the industrial town of Mahad, 165km south of Mumbai. - AFP