There have been two large explosions near to where former Pakistan Prime Minister Benazir Bhutto was being welcomed home.
She was unhurt and is safe but a number of people have been reported injured close to her procession in Karachi.
Ms Bhutto was in a truck on her way to a rally near the tomb of Mohammad Ali Jinnah, the founder of Pakistan, when the attacks happened.
The vehicle had just passed when the bombs went off, and there is speculation that at least one of the attacks was a car blast.
Ms Bhutto was evacuated from the truck and Sky News' Foreign Affairs Editor Tim Marshall said "she had gone to a house she knows well".
It is not known whether she will attend the planned rally.