According to Dawn sources, the cylinder was installed on a minibus which was waiting in line for its turn at a CNG filling station in Mubina town area of Karachi.
All injured were shifted to a nearby hospital.
The windows of cars and houses in the vicinity were shattered as a result of the blast whereas panic and fear gripped the area after the incident.
The blast also caused damage to the filling station and parked cars.
Police cleared the area and shifted the damaged bus from the site.
Traffic on one lane of Abul Hasan Ispihani Road was suspended to facilitate the rescue activities.