The attack took place in the city of Quetta, the capital of Baluchistan province. Police declined to say who they suspected in the latest blast to rock a region that is frequently hit by acts of violence.
Islamist militants often attack security force or government targets, as do separatist rebels, who also kill settlers from other parts of Pakistan. Sunni extremists also frequently kill Shiites in the region, sometimes pulling them off buses and gunning them down.
The bus targeted Monday was heading to the Baluchistan University of Information Technology in an upmarket neighborhood of Quetta.
Police officer Mir Zubair Mahmood said five students on the bus were killed and scores were wounded, as were several passers-by.