The first blast occurred outside an imambargah (Shia prayer hall) in Abbas Town at about 7 P.M. as people were leaving after prayers. The second explosion went off in the same area within 10 minutes, local residents said.
Officials at three hospitals said 37 people, including women and children, were killed in the attack.
Jinnah Hospital alone received 20 bodies and several seriously injured persons. Officials at Patel Hospital said they had received eight bodies and four more people succumbed to injuries in hospital.
About 80 people were injured and an emergency was declared at hospitals across Karachi. Several young children were among the seriously injured, officials said.
Police officials said the first blast was apparently caused by explosives hidden in a car that was parked near the entrance of Abbas Town.
Residents of Karachi said the explosion was heard from 10 km away. The bomb was packed with ball bearings, which caused widespread damage. There were reports that the second blast was caused by the gas cylinder of a car, though this could not immediately be confirmed.
The blasts caused a power outage and triggered panic in Abbas Town, which has a large Shia population.
The explosions destroyed the facade of two apartment blocks and damaged about 20 shops and several cars.
Fires erupted in the apartment blocks and footage on television showed huge flames leaping into the night sky.
Local residents used car headlights to help rescuers who searched for survivors in the rubble of apartments and shops that were destroyed by the blasts.
Many people complained that rescue teams and the fire service took an inordinately long time in reaching the site of the blasts.
Heavy machinery reached the spot almost two hours after the attack and residents rushed the injured to hospital in private vehicles and auto-rickshaws.
Local media reports said security forces and senior officials were engaged in providing protection for the engagement ceremony of a senior aide of the Sindh Chief Minister and this hindered rescue operations.
Many top leaders of the Pakistan People's Party, including Prime Minister Raja Pervez Ashrag, were in Karachi to attend the engagement.
No group claimed responsibility for the attack.
The banned Lashkar-e-Jhangvi has claimed a string of recent attacks on Shias in other parts of Pakistan, including the south-western city of Quetta.
Abbas Town has been the target of terrorist attacks in the past too.
On November 18, three persons were killed and more than 20 injured when a bomb went off outside an imambargah in the area.
Last month, 91 people were killed in a bomb attack on a Shia area in the south-western city of Quetta.
President Asif Ali Zardari and Prime Minister Ashraf condemned the blasts.
Ashraf ordered an inquiry into the incident and said those "targeting innocent civilians are serving the interests of anti-state and anti-social elements".
The premier cancelled his official engagements and began overseeing rescue and relief operations.
The Sindh government announced a day of mourning tomorrow while Shia groups called for a shutdown.
Officials said all educational institutions in Karachi would be closed tomorrow while traders associations called for markets to remain shut to protest the attack.
Karachi: Thirty-seven people, including women and children, were killed and about 80 injured when two blasts ripped through a Shia-dominated area of the southern Pakistani port city of Karachi on Sunday, the latest in a string of attacks targeting the minority sect.
First Published: Sunday, March 03, 2013, 21:04