A bomb exploded in a crowded area of Pakistan's southern port city of Karachi on Tuesday, killing at least one person and injuring 21, police said. Two of the injured were in critical condition, said a police spokesman. It was not immediately clear who was targeted by the blast in the Aisha Manzil area of Karachi. The explosion was heard several kilometers away. Karachi is home to 18 million people and is the financial capital of Pakistan.