The incident "seems to be a suicide blast", Dawn reported quoting Quetta Senior Superintendent of Police (SSP) Operations Mohammad Baloch.
Probe is underway to detect the cause of the blast.
About 100 people were present on site when the blast took place.
#BREAKING: 21 killed and over 30 injured in a bomb blast at Quetta Railway Station in Balochistan. Baloch Liberation Army claims responsibility for the attack on Pakistan Army’s unit while they were in Jaffer Express Train. Casualties likely to increase. pic.twitter.com/ob2on4rJ7M
— Aditya Raj Kaul (@AdityaRajKaul) November 9, 2024
The blast occurred on the platform at the railway station when a train was ready to depart for Peshawar.
Police and security forces have reached the site.
The toll is expected to rise as several wounded passengers are critical.