KARACHI, Pakistan—The death toll from a sewer gas blast in Pakistan’s largest city of Karachi jumped to 17 as some critically injured people died overnight and Sunday, police said. Initially, 12 people were reported dead and 11 others injured in Saturday’s gas explosion in a sewage system in the commercial hub of Pakistan Saturday. Senior police officer Sarfaraz Nawaz Shaikh said the loss of lives and property could be blamed on human errors of construction over the sewer. He said the number of injured also increased to 16. The blast destroyed the HBL bank building constructed over the sewer. The building was one of several ordered to vacate after violating building laws, according to Mukhtar Abro, a local administrator, who said the structures were to be demolished in coming weeks. Many sewage channels in the city have been covered, mostly illegally, by constructing concrete structures over them. Also Sunday, a …