The blasts occurred in Aziz Abad area of Karachi and near the office of the Mutahida Qaumi Movement (MQM) close to the central headquarters of the party.
Hospital sources said that eight persons were shifted to the hospital.
Second blast occurred when the rescue teams were busy in shifting the injured to hospitals.
The blast injured several rescue members and media persons.
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The MQM headquarters is also located the blast site, residents said.
The blast created panic in the area and the traders shut down shops. Power supply was also suspended in the area.
This is the sixth time in the last two weeks that bomb attacks have been carried out close to MQM election/sector offices in Pakistan's biggest city.