The violence Tuesday was largely centered in the port city's Orangi Town, but spread to other sections of the city, Dawn newspaper reported.
The city imposed a ban on "pillion riding," referring to motorcycles carrying passengers on back seats as most of the killings are carried out through drive-by firings by such riders.
Karachi police said gun battles erupted after an attack that injured the district information secretary of the Awami National Party in Orangi Town. A three-day wave of violence in the city last month -- blamed on political, sectarian and ethnic motivations -- left 23 people dead.
Karachi, capital of Sindh province and also Pakistan's financial center, has been the scene of such violence for months, resulting in the deaths of hundreds despite numerous security measures.
The violence has largely involved members and supporters of the Urdu-speaking Muttahida Qaumi Movement and the ANP representing ethnic Pashtuns, with both sides blaming the other for starting the violence. The city's woes are separate from the widespread militant clashes in other parts of the country.
The Human Rights Commission of Pakistan expressed grave concern over the worsening situation in Karachi, where such targeted killings are on the rise.
The group said a total of 1,138 people died in the city in the first six months of this year as a result of targeted and other forms of violence.
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