A five-story building collapsed, killing at least 21 people, mostly women and children, authorities said Saturday.
Mayor Mohammad Dilawar, who was supervising the rescue work, said the building caved in late Friday in the congested downtown Lea Market neighborhood.
A district government official, Masood Alam, said 21 bodies had been retrieved from the debris and that the toll could rise. "We have so far removed almost half of the rubble."
Rescue teams were having trouble moving through the narrow streets in the area. The building apparently was weakened by heavy monsoon rains, Dilawar said.
Karachi, a city of more than 16 million people, has an aging infrastructure and a poor drainage system.