Police officials told the media that the incident occurred outside an imambargah at Orangi town in Karachi this evening.
Evidence gathered from the site, suggested the rider of the motorcycle was a suicide attacker whose explosives had gone off after his vehicle collided with an auto rickshaw.
Police officials had collected body parts and other evidence from the site.
Two persons were killed and several others injured, witnesses and police officials told TV news channels.
Footage on television showed a motor cycle and an auto rickshaw that were destroyed by the blast.
The explosion damaged nearby buildings and shops.
No group has claimed responsibility for the incident.
Security has been tightened across Pakistan to avert possible attacks on Shia gatherings in the Islamic month of Muharram.
On Sunday, in a similar attack, four persons were killed and more than 20 injured when a bomb went off outside another Shia imambargah in Karachi.
The blast had occurred near the imambargah in Abbas Town area of Pakistan's largest city.
