The city has the world’s second-largest collection of the buildings, second only to Miami. But even as they gain attention, they are threatened.

These architects broke with the British Raj’s ornate Victorian Gothic and Indo-Saracenic styles for the latest international trend — described by a leading British architect as “the nudist movement in our profession” — while adapting it to the local environment. The choice could be seen as a form of resistance, said Mustansir Dalvi, professor at the Sir J. J. School of Art and Architecture, and as a backdrop of the freedom movement.

Movie houses, many built by American movie companies like MGM, glamorized the new aesthetic. A new technology, reinforced cement concrete, made all this construction quick and cheap. The apartments were snapped up by a rising urban elite “who aspired to be modern and were willing to live next to those who were not like themselves,” said Mr. Dalvi. “They sat next to each other in offices, on commutes, in cinema halls.”

He adds: “For Bombay, what Art Deco represents is cosmopolitanism.”