A 12-year-old boy was killed today and six members of his family injured in one of two bomb blasts in the Pakistan port city of Karachi, police said.

Pakistan's largest city remains tense as polls opposed by powerful ethnic groups open for local Government elections after a night of violence in which five people have been killed.

Two bombs have exploded killing two people in Karachi as a strike called by two militant ethnic-based parties paralysed Pakistan's Sindh province.