The explosion must have taken place in the ticket hall at 9 o’clock on Saturday morning, according to initial information.
20 people have died and another 30 people are injured, according to the TV channel Geo News.
Police believe it may be a suspected suicide bombing, but this has not yet been confirmed.
The crime took place in Quetta, in the province of Baluchistan. Previous attacks in the area have often been carried out by separatist militia groups whose goal is for Baluchistan to break away from Pakistan, reports the news agency TT. There have also been attacks by the Pakistani Taliban and by groups linked to al-Qaeda and IS.