While the premier held meetings with top officials of the Intelligence agencies and Director-General Rangers in Karachi to discuss operations to clean up the city, the killings took place near National stadium, Baghdadi (Lyari), Machar Goth, Old Haji camp, Orangi town and Patel para.
Those killed included Pakistan Navy Captain, a police officer, a Ranger and a prayer leader of a mosque.
"A local mosque prayer leader, Saleem, a passerby Amad and a police constable Aziz were killed in the firing," he said.
A Rangers spokesman said one of their soldiers was killed in the operation.
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Early today, unknown gunmen opened fire on the car of Pakistan Navy Capitan Nadeem near National stadium.
"Nadeem was with his wife and both were critically injured. Nadeem later died in hospital while his wife is in critical condition," SSP Imran Shaukat said.
Police said that two bodies were recovered from Patel Para and Haji camp while one person was killed in a targetted attack in Machar Goth.
Prime Minister Sharif told the top officials of the Rangers and Intelligence agencies in the meeting that all no-go areas in the city must be abolished.
Sharif was quoted by television channels as saying that the time for half hearted efforts to control the law and order situation was over and force would be used to ensure peace and security returns to the Karachites.
Pakistan's biggest city has become a hub of criminal and militant activities with targetted killings, kidnappings, extortion rackets and land grabbing assuming a epidemic nature since last year.
Political parties blame each other for harbouring and supporting militant and criminal groups.
At least 2,084 people have been killed in the first eight months this year according to Karachi police chief Ghulam Qadir.