No one claimed responsibility for the attack on Thursday on the underground pipe near Dadhar town in Baluchistan province but ethnic minority fighters battling for political and economic autonomy have in the past claimed such attacks.
Police official Ali Akbar said explosives were used in the blast that left a 2m crater. Dadhar is 100km southeast of the provincial capital, Quetta.
Amir Muhammad Dutani, an official of the state-run Sui Southern Gas Co Ltd distribution firm, said supplies were disrupted to nearby areas.
Tribal fighters have been waging a low-level insurgency in Baluchistan for decades but they have stepped up attacks on government installations including gas and transport facilities in recent weeks.
They say profits from Baluchistan's gas reserves go to outsiders and the people of the province, Pakistan's biggest but poorest, are neglected.
In January, supplies from Pakistan's biggest gas field, at Sui in Baluchistan, were cut for more than a week after a bloody attack.