The explosion in Korangi completely destroyed the courier company's office though there was no loss of life reported as there was no one present at the site at the time of blast, according to Landhi SP Faisal Noor.
Emergency and rescue teams reached the site after the blast.
Bomb Disposal Squad personnel said 500 grams of explosive material was used in the explosion.
Prior to this attack, three attacks have taken place on the offices of the same company during the past two months.
In another unrelated incident, unknown gunmen opened fire at a policeman near Maymar complex in Gulshan-i-Maymar area of Karachi.
The police constable succumbed to his wounds while being shifted to a hospital for treatment.
The deceased was deputed at the Ajmer Nagri police headquarters.
Meanwhile, a two-day-old body of a man was recovered from Lyari River.