Sources told Business Recorder that four people were sitting on the footpath near "North Over Bridge Gate" known as NOB Gate at East Wharf, when one of the persons tried to pick up a shopping bag lying on the footpath which exploded at about 7.30 pm.
The source said, "It is to early to say the motive behind the incident, but the explosive material has roughly about 200 grams of weight".
All the four injured were rushed to Civil Hospital Karachi (CHK) for medical assistance by Edhi ambulances.
Later, one identified as Fateh Mohammed died of wounds in the hospital and his brother Nasrullah is stated to be in precarious condition.
The other two injured were identified as Jameel Mohammed and Tariq.
The sources said investigators were looking into the explosion and are sharing expertise of other sensitive agencies as well as explosive experts in this regard.
Provincial Police Officer Syed Kamal Shah accompanied with CCPO Asad Ashraf Malik told newsmen that the blast occurred on the footpath where labourers and loaders were working on containers.
Kamal Shah said it might be targeted, but we have to ascertain when the terrorists reached at this point after crossing all the security checks.
The place of blast is the busiest part of Karachi Port where mostly import cargoes were handled.