Members of Pakistan's Shia community have been digging through the rubble of a massive car bombing in Karachi looking for loved ones as the death toll from the blast climbs to 45.

The explosion yesterday targeted members of the minority sect leaving a mosque in the port city.

The blast underlines the increasing threat faced by Shias as Sunni militant groups target them in ever-bolder attacks.

At least 146 people were also injured in the explosion with 32 of them in a serious condition.

There was no immediate claim of responsibility but Sunni militant groups who do not consider Shias to be true Muslims have carried out such attacks in the past.

This was the third mass casualty attack since the beginning of the year against Shias.

The first two killed nearly 200 people in the southwestern city of Quetta, which is home to many Hazaras.

They are an ethnic group, mostly made up of Shia Muslims, who migrated from Afghanistan more than century ago.

Those attacks were claimed by Lashkar-e-Jhangvi, a Sunni militant group known for its virulent hatred of Shia Muslims.

Pakistan's intelligence agencies helped nurture Sunni militant groups like Lashkar-e-Jhangvi in the 1980s and 1990s to counter a perceived threat from neighbouring Iran, which is mostly Shia.

Pakistan banned Lashkar-e-Jhangvi in 2001, but the group continues to attack Shias.

Karachi shut down for a day of mourning to honour the dead.

Markets, gas stations and transportation were closed as security officials patrolled the streets.