Police said explosive devices placed under the pipeline were detonated, causing a fire, Pakistan's Dawn News reported.
The blast, in the Dera Murad Jamali area, cut off gas supplies to the provincial capital, Quetta, and several other districts.
Rescue workers extinguished the fire in about four hours.
Officials said gas to the affected areas should be restored in about 24 hours.
Separately, at least one person died and three others were injured in a gas explosion at a home in Quetta, the News International reported.
Police said a heater leaked gas into a room of the house, and the gas exploded when someone lit a match.
The house was badly damaged.
Pregnant Mila Kunis wins 'Best Villain' at MTV Movie Awards
'Happy' fan videos make Pharrell cry [VIDEO]