The death toll, it is feared, could mount as some of the injured are reportedly in critical condition.
According to an eyewitness, the bomber, dressed in black, tried to enter the procession and blew him up when he was asked to stop by police and volunteers. Another eyewitness said that hand grenades were lobbed at the procession followed by the suicide blast.
Rescue teams rushed to the scene and shifted the injured to hospitals, where emergency has been declared.
The blast also caused a blackout in the area.
Hundreds of worshippers, beating their heads and chests, kept marching, even though seven hand grenades were found at the site.
The attack came hours after two bomb blasts killed at least two people near a gathering of Shia mourners in Karachi. SAMAA