The accident happened in a ready-mix plant (mixing unit for building materials) Tuesday night here in sector 90.
Police official Aman Singh told IANS: "Over half a dozen labourers were having bath and washing their clothes in Kankrola village here, under Kherki Daula police station, late Tuesday night when suddenly a water tank collapsed on them."
"Three people died on the spot while another succumbed to his injuries on the way to the hospital," he said.
"All the victims were males and are yet to be identified. We have registered a case against the manager and the management under Section 304 A of the Indian Penal Code (causing death due to negligence)," he added.
One critically injured person was admitted to a private hospital. Some other people suffered minor injuries.
No one was arrested.
"We are investigating the case," the official added.