The mishap occurred yesterday at Ranjanpur village in neighbouring Nandurbar district, when they were drinking water from the tank after attending a Mahshivratri fair, they said.
The cement tank caved in after it suddenly developed cracks, trapping the victims under the debris, police said.
The injured have been admitted to a hospital, they said.
The deceased, all tribals from nearby hamlets, have been identified as Subhash Sonawane (55), his son Ravindra (5), Rahul Palve (35) and Amar Singh Vasawe (45), police said.