The gunmen fired indiscriminately at the taxi in which five men were going from Quetta to the suburb of Hazara Town. They fled after the shooting.
The dead and injured were taken to a nearby hospital.
Security forces cordoned off the area and conducted a search but were unable to make any arrests.
Officials described the incident as a targeted attack on members of the minority Hazara Shia community.
No group claimed responsibility for the incident though such attacks are usually blamed on the banned Lashkar-e-Jhangvi, which has killed dozens of Hazara Shias across Balochistan province over the past few months.