All shops, markets, petrol pumps, tea stalls and 'paan' kiosks shut down after the announcement by the Muttahida Qaumi Movement (MQM) central committee at a press conference.
"We have decided to shut down business voluntarily because we anticipate there could be violence and rioting," shopkeeper Ahmed Raza said on the deserted I Chundrigar road.
MQM's senior leader, Khalid Maqbool said the day of mourning was being observed as for months now party workers and supporters were being kidnapped and the police and rangers were not showing their arrests in court.
He said the MQM had shown patience and tolerance for months now despite the growing incidents against their workers and supporters.
"But we feel enough is enough and we will be observing a day of mourning tomorrow to convey our sentiments," he said.
They were reports of firing and rioting from different areas of the city soon after news of the bodies being identified as MQM workers spread.
The MQM which represents the Urdu-speaking population which migrated from India after Partition, is the single largest party in the city and last week joined the ruling Pakistan Peoples Party (PPP) in the provincial government.
Maqbool said workers had been told to remain peaceful.
