Police said the bomb had been planted in a red charade car and was detonated by a remote device in Mahmoodabad area near a bakery last night.
"They were a lot of people around the bakery at the time of the blast most of them involved in the electioneering campaign of a political party," a police official said.
The injured were rushed to Jinnah hospital, where their condition was stated to be stable.
The blast spread fear among local residents and was so loud that it was heard from far away. Nearby shops and vehicles were also damaged in the incident.
The outlawed Tehreek-e-Taliban have threatened to carry out attacks against these parties and the Pakistan People's Party because of their secular policies.