Tension gripped this largest city of Pakistan after at least 25 people were killed in ethnic violence, authorities said.
"Panic gripped parts of the city as unidentified attackers went on a shooting spree, killing most of the victims at point-blank range," Dawn reported on Thursday.
City police chief Wasim Ahmed said 20 people were killed on Wednesday in the violence across the city, including "16 Pathans and three Urdu-speaking people".
Police said that the trouble had begun early in the morning when armed men who had taken position on the hills in north Karachi fired shots at Zarina Colony, a shanty town in the foothills. A worker of the Muttahida Quami Movement was killed at around 10.30 am.
Police said that a sub-inspector and a constable were shot and wounded when law-enforcement personnel went to get the body.
Superintendent of Police of North Karachi, Farooq Ahmed, said police and Rangers returned fire, forcing the gunmen to retreat.
"Later, police and Rangers conducted a siege and search operation on the hills, arrested 16 people and seized some weapons," he added.
Most of the violent incidents took place in Khawaja Ajmair Nagri, Surjani Town and New Karachi Industrial Area. The violence-hit areas wore a deserted look as shopkeepers pulled down their shutters.
An MQM worker was shot dead in Shah Faisal Colony. His body was first taken to the Jinnah Postgraduate Medical Centre (JPMC) and then to the Abbasi Shaheed Hospital for postmortem examination. Police surgeon Hamid Padhiar told Dawn that 12 people were brought dead to the Abbasi Hospital.
The director at the emergency centre of JPMC, Seemin Jamali, said 11 bodies and 18 wounded people were brought to the hospital. "Four wounded victims later died," she added.
Civil Hospital's medico-legal officer Sarwat Channa said that a man was brought dead from North Nazimabad and another man from Teen Hatti.
Sources said that two bullet-riddled bodies were found at a post office in Sachal area. The bodies were taken to the JPMC late in the night.