About 50 people are feared trapped under the debris and rescuers scrambled to save them, said an official.
Situated near the Dockyard Road in south Mumbai, the building is a civic employees' staff quarter. It is at least five-decades old.
It suddenly collapsed around 5.45 a.m, catching a majority of residents in their sleep, the official said.
A few years ago, it had been declared extremely dilapidated and had been examined by a team of BrihanMumbai Municipal Corporation (BMC) that recommended urgent repairs and shifting of the families living there.
"There were 28 rooms on the four floors of which 22 were occupied by civic employees and their families, besides a godown on the ground floor where several labourers were living. The delay in shifting out the residents to transit camps and carrying out repairs has led to the avoidable tragedy," claimed Suresh Jadhav, a former municipal corporator from the area.
Mumbai Mayor Suresh Prabhu said priority is to rescue those who are trapped and efforts were continuing on a war-footing.
--IANS (Posted on 27-09-2013)