The building collapsed at around 2:30 am (2130 GMT Monday) in the port city of Karachi, where rescue workers are still searching for survivors.
"Six people including a woman and a child were killed and 10 others were injured in the incident," Deputy Commissioner Fariduddin Mustafa told dpa.
The injured, including five women, have been shifted to a nearby hospital for treatment.
The rescue workers are avoiding the use of heavy machinery in the search for survivors, but there are limited chances of survival under the tons of rubble.
The cause of the collapse is not yet known, and it may take 24 hours to remove the debris, Mustafa said.
The number of people living in the commercial-cum-residential building is also not known, he said.
Local media reported that the building was old and not safe for living.
The provincial government issued eviction notices to residents of more than 300 unsafe buildings in the city last month, but this building, according to reports, was not on the list.
Safety codes for the construction of buildings are often ignored in Pakistan.
Pakistani rescue workers search for victims as they remove debris after a three story building collapsed at a residential area in Karachi.
At least six people were killed and 10 others were injured in southern Pakistan when a three-storey building collapsed in the early hours of Tuesday, an official said.
