Following Wednesday's killing of 13 people including ex-MP Waja Karim Dad, violence escalated and officials say more bodies were recovered overnight.
Police say many of those killed were kidnapped first and that some victims appear to have been tortured.
The attacks unfolded as Karachi's main MQM political party announced it will rejoin Pakistan's coalition government.
The party had left the PPP-led coalition after accusing its majority partner of not doing enough to stop the violence.
Police say that 315 people were killed in such attacks in Karachi in July 2011.
The BBC's Syed Shoaib Hasan in Karachi says that the bodies are appearing all over the city stuffed in jute bags.
Our correspondent says that while initially politically motivated, the killings are now increasingly indiscriminate. Women, children and teenage footballers are amongst those gunned down.
Police say that the bodies bear the marks of extreme torture: some have even had their eyes gouged out. They said that it appears as if almost all the victims were kidnapped before being tortured only to be shot dead and deposited on the city streets.
Police surgeon Hamid Parihar told the BBC that he "had been collecting bodies since midnight and they are still coming in".
Analysts say that the latest spate of violence appears to have taken place between criminal gangs in the city's deprived Lyari neighbourhood. The area has a reputation of armed gangs dealing in drugs and extortion rackets.
This is where former parliamentarian Waja Karim Dad was gunned down.
Our correspondent reports that a sense of fear prevails throughout the city and that public transport has been suspended.
Killings in Karachi have continued despite efforts to reconcile its warring political factions.
Security officials say this is because the killers are being protected by senior politicians.
They say the violence is being used to stoke recently ignited ethnic passions both for political gains and as a means by criminal gangs to fight turf wars behind the facade of political activism.
At least 39 people have been killed in two days of political and gang violence in Pakistan's southern city of Karachi.