Police officials said that the killings had taken place in different localities and the casualties included political activists.
Scores have also been injured in incidents of firing and violence over the last 24 hours.
The fresh round of bloodshed that started yesterday when nine people were killed, went on today with the total number of those killed increasing to 18.
One police official said that a political activist was shot dead by unknown armed men in the New Karachi area, while a body of another activist was found in the Shirin Jinnah Colony.
Two others, also belonging to a political party, were injured in Korangi.
An activist of Muttahida Qaumi Movement (MQM) was killed at Safora Goth within the limits of Gulistan-e-Jauhar police station.
Police officials said that the deceased identified as Shakeel aka Mamu, was sitting in front his house when two men riding on a motorcycle targeted him.
He was taken to Jinnah Postgraduate Medical Centre where he succumbed to his injuries.
Meanwhile, a personnel of the Pakistan Navy succumbed to his injuries during treatment at JPMC.
He was injured near Natha Khan Goth within Shah Faisal Colony police station last night. He was identified as Kamran Ali.
Police officials said that the incident took place when a group of criminals opened fire at the police mobile near Natha Khan Goth in which a police head constable named Ghulam Raza was killed while the Navy personnel who was passing from there was injured.
Police and the para-military rangers have been carrying out targeted operations in some parts of the city to arrest target killers and extortionists.
In a police operation, security personnel arrested three extortionists and a killer accused of murdering a member of a political party.
According to DSP Wasif Qureshi, two extortionists -