All private and government schools remained closed and the examinations were postponed while public transport also remained off the roads with markets, petrol pumps and other businesses shutdown during the strike.
The blast at the MQM election camp office here last night killed three people and wounded 18 others.
In a statement from London, MQM chief Altaf Hussain said that in such insecure conditions it would be difficult for the people to come out of their homes and caste their votes in the General Elections on May 11.
The MQM is the largest single party in Karachi and in the last elections it got 25 national assembly seats from Pakistan's financial hub.