The explosion occurred outside an imambargah at Orangi town in Karachi this evening, witnesses said.
The exact nature of the blast could not be immediately ascertained.
One person was 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.
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.