Rescuers are searching for three people feared trapped in the debris of the building which came down in Mumbai's Thane district, a spokesman said.
The cause was not immediately known but Mumbai has been hit with heavy monsoon rains.
Ten days ago, another building collapse in Mumbai left 10 people dead.
In April, 74 people were killed when an eight-storey building being constructed in Thane caved in. It was the country's worst building collapse in decades.
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