The patient, a 56-year-old man, had no travel history and was admitted to a local hospital with a fever on Sunday and tested positive for the new coronavirus on Wednesday, an official of the Brihanmumbai Municipal Corporation (BMC) said, according to Al Jazeera.
The authorities have sealed the building where he lived, which is located in a redeveloped part of the Dharavi slum, local media reported.
Also, seven members of his family were quarantined and tested on Thursday for the virus that causes the COVID-19 disease, the Xinhua news agency said.
Mumbai authorities are concerned over the possible spread of the new coronavirus, as Dharavi is known as the most densely populated slum in Asia. At the same time, a doctor and a worker from a municipal corporation also tested positive.
An estimated 700,000 to 1 million people live crammed in Dharavi - a roughly five-square-kilometer maze of narrow lanes, dilapidated buildings, huts, and open sewers.
Public health experts say it would be difficult to contain the virus if it spread in a slum-like Dharavi where eight to 10 people often share a room.
The population density is about 270,000 per square kilometer, making social distancing almost impossible. Scores of people share water sources and sanitation facilities, Al Jazeera reported.
Dharavi's cases have raised concern that India may be experiencing community transmission of the disease despite a countrywide lockdown since March 25, as well as exposing the harsh reality and problems of inequality in the country.
For his part, Prime Minister Narendra Modi insisted that "testing, isolation and quarantine" will remain priorities in the coming weeks, ignoring the situation of places like Dharavi, the problems of its population, as well as the needs that have arisen in the public health system in the country.
The death toll due to the COVID-19 in India stands at 62 as of Thursday, according to the latest data, while the number of confirmed cases in the country is around 2,547.