The mishap took place at around 8.13 AM in the Indira Nagar area, they said.
Some persons were inside and a few others were waiting outside the public lavatory when suddenly a portion of it caved in. As a result, some persons slipped into the septic tank, an official from Brihanmumbai Municipal Corporation's disaster control room said.
"Our control room got the call at 8.13 AM. We immediately informed the fire brigade department. A team of fire brigade personnel reached the spot and retrieved three bodies," he said.
Mankhurd police are on the spot and further investigation is on, Mumbai police spokesperson Ashok Dudhe said.
More From This Section
The incident occurred in a slum area where the lavatory was used daily by nearly 5,000 people.
When contacted, a senior civic official said the toilet was maintained by Maharashtra Housing and Development Authority (MHADA).
Local residents blamed the authorities for not paying attention to the complaints filed several times by them about the pathetic condition of the toilet.
Further details are awaited.