The blast took place in a slum at Golibar in Santacruz (East).
One injured person, who sustained nearly 90 per cent burns in the mishap, was admitted to Kasturba hospital, while the two others hurt were rushed to V N Desai hospital, an official at Santacruz police station said.
The deceased were identified as Rajdev Dixit (45) his brother Kapil Dixit (40), and his sons Yashwant Dixit (17) and Jeetu Dixit (20).
The cause of the blast was yet to be ascertained, police added.