At least three people were killed and 12 others injured when a dilapidated three-storey building collapsed in a poor neighbourhood of Karachi, Pakistan police said.
Senior official Aran Kobra said the dead included a man and his son, who were asleep when the apartments collapsed before dawn on Tuesday.
He said up to two other people were believed to be trapped under the rubble.
"We are using heavy machinery with care as we have information that one or two people are still trapped in the rubble," he said.
TV footage showed a teenage boy crying for help as residents struggled with their hands to remove a concrete pillar that had fallen on his leg.
The boy was later rescued with the help of construction machinery.
Earlier, Karachi's Deputy Commissioner Farid Uddin said the death toll could climb as rescue workers carefully sifted through the rubble.
He said the cause of the collapse was not immediately known, though reports indicated the building was old and poorly constructed, which could have contributed to the collapse.
Safety codes are often ignored in Pakistan and in some of the poorer areas construction is haphazard and bribes are paid to inspectors to approve substandard construction.