A car bomb in a mainly Shiite Muslim area of Karachi on Sunday killed at least 30 people, police said, the deadliest attack in Pakistan's largest city in three years, just two weeks before parliament is due to be dissolved for elections.
The blast badly damaged two five-storey residential buildings in the Abbas town area, which is dominated by minority Shiites, setting one on fire, but police said the target of the attack was not yet clear.
Karachi is plagued by sectarian, ethnic and political violence, with more than 2,200 people killed in shootings and bombings last year, but major bomb blasts are relatively rare.
"At least 30 people were killed in this bomb blast, three of them were policemen," Fayaz Lughari, police chief of Sindh province told AFP, warning that the death toll could rise. More than 50 were injured.
Ijaz Ali was on the third floor of one of the blocks of flats with his wife and two sons when the bomb went off.
"All of a sudden I heard a huge blast and we thought the building was going to collapse -- it was like an earthquake," he told AFP from hospital.
"The windows of my flat exploded towards me, something hit my head and knocked me unconscious. I opened my eyes in hospital and I am just relieved that my family survived."
Violence against Shiites, who make up around 20 percent of Pakistan's 180 million population, has reached record levels, raising serious questions about security as the nuclear-armed country prepares for elections due by mid-May.
More than 400 Shiites were killed in sectarian attacks in 2012, according to rights groups, and two deadly bombings targeting the minority in the southwestern city of Quetta have already killed nearly 200 this year.
On Monday a bomb at a Sufi shrine regularly visited by Shiites in southern Shikarpur district, some 400 kilometres (250 miles) northeast of Karachi, killed two people and wounded 10 others.
A day later the Supreme Court ordered the authorities to come up with a strategy to protect Shiites after a wave of bloody attacks in the southwest.
Two major bombings in the space of five weeks targeting Shiite Hazaras in Quetta, capital of Baluchistan province, which has been a focus of sectarian violence, killed nearly 200 people.
Both attacks, the most recent on February 16, were claimed by the banned extremist Sunni group Lashkar-e-Jhangvi, and have highlighted the government's inability to stem sectarian violence.
The Pakistani Taliban have also increased their campaign of violence in recent months, leading to fears that violence could mar a general election scheduled to take place by mid-May.
Last month the group proposed talks with Islamabad but the government insists the militants must declare a ceasefire before coming to the negotiating table -- a condition militants have rejected.