The injured were admitted to Sanjeevani Hospital in Virar. Three of them, who were in a critical condition, have been shifted to KEM Hospital at Parel.
According to sources, three of the deceased have been identified as Majunath, Govind and Maju. The identity of the fourth person is yet to be ascertained.
Sources said the blast was so powerful that it damaged the compound wall, the roof of the godown and the surrounding structures.
The Virar police have registered a case of accidental death and are investigating the incident. Sources said the blast allegedly took place during the illegal transfer of gas from one cylinder to another.
However, a senior police official did not confirm the same.