According to the city Disaster Control, a slab of the building Khatija Manzil on Mohammed Ali Road collapsed around 4.45 pm.
Imtiaz Siddiqui, 28, and Maleshwar Mahanto, 29, were killed instantly.
Rafique Shaikh, 40, and Kalam Shaikh, 25, who were injured, died early Saturday in a hospital.
Work to clear the debris continued Saturday though authorities are not certain whether more people are trapped in the debris.
Police have lodged a complaint against the building owner Farrukh Yusuf Batki and detained him.
The casualty figures could have been higher but for the timely action by authorities.
Around 3 p.m., a wide crack was noticed in the building and by 4.30 p.m., most residents were evacuated.
Mumbai: The death toll in Friday's building collapse in south Mumbai climbed to four with two more injured succumbing here early Saturday, officials said.
First Published: Saturday, February 16, 2013, 14:36