The report by the census 2011 says that there are more than 4 lakh empty apartments in Mumbai. More information will be available at 'More than 10% apartments in Mumbai are vacant', a report in commonfloor.com
It is reported that the number of empty apartments are higher in Mumbai. However there are some apartments whose owners are stayed away. There are few unsold. Few apartments may have individual owner. Most of them are still under the builders