The attack occurred in the afternoon, as about 20 Shia Muslims were on their way to a mosque for Friday prayers, said Athar Rashid Butt, a senior police official in the city.
Some of the wounded were in critical condition.
Nobody claimed responsibility, but suspicion fell immediately on one of several Sunni Muslim extremist groups which have killed hundreds of minority Shias over recent years.
The attack occurred in a neighbourhood in the west of the city, near the city's port.
Police said an investigation was underway, but that no arrests had been made.
Most of Pakistan's Shia and Sunni Muslims live peacefully together, but extremist groups on both sides are responsible for many attacks.
Sunni Muslim suicide attackers stormed a mosque in the southwestern city of Quetta in July, killing around 50 worshippers.
A month earlier, gunmen opened fire on Shia police trainees in the town, killing 11.