The ECP statement followed a series of rigging allegations levelled by many political parties against each other in the port city, Dawn News reported.
Balloting in the city were also marred by two blasts and other incidents of violence at polling stations.
Even as voting time across the country was extended by an hour, the ECP gave three more hours for balloting at seven Karachi constituencies.
At least 10 people were killed and 50 others injured in a huge explosion that tore through a group of voters waiting near a polling station in Quaidabad area.
The Mohajir Qaumi Movement, Sunni Ittehad Council and Jamaat-e-Islami boycotted the polls in Karachi.
The Pakistan Tehreek-e-Insaf said there was rigging in several areas of Karachi and that the MQM was involved in it, Radio Pakistan reported.
--IANS (Posted on 11-05-2013)