At least three people were killed and four others injured when a bomb exploded outside a commercial plaza in Pakistan's southern port city of Karachi on Wednesday night, local media reported.

Local Urdu TV channel Dunya quoted unknown police sources as saying that the bomb was detonated by a remote control outside a commercial plaza in Sohrab Goth area of Karachi, the largest commercial hub of the country.

The explosive materials were fixed at a motorbike.

Some other media reports said that the target of the bomb was a drug den and the affected people were druggies who were gathering in the area for taking drugs.

No group claimed responsibility for the blast yet.

Police and other law enforcement agencies cordoned off the area and an initial investigation into the incident has started.

Following the blast, police kept media and other people at a distance of few yards from the blast site for security concerns, as after a minor blast earlier on January 25, when police and residents gathered at the blast site a second blast took place, killing six people and injuring several others.