Sui Southern Gas said on Tuesday the blast destroyed about 65m of the pipeline near the southern city of Nawabshah, disrupting gas supplies in the northeastern part of Sindh province.
There were no reports of any casualties.
Disgruntled Pakistani tribesmen have bombed natural gas pipelines several times this year. On Saturday, suspected tribesmen fired 16 rockets at a state-run natural gas facility in southwestern Pakistan and damaged a main pipeline.
A statement from Sui Southern said Tuesday's explosion was so powerful that one nine-metre section of pipeline was blown a distance of 100m.
It said block valves upstream and downstream from the site of the blast were immediately closed to prevent any major loss of gas. Nawabshah is about 200km northeast of Pakistan's main port of Karachi.
Security stepped up
Sui Southern said repairs to the pipeline would take 36 hours, but supplies to affected areas were expected to be restored on Wednesday afternoon.
The firm said it had stepped up security surveillance of the pipeline and police had been deployed to key installations. It called on the provincial and national governments to ensure pipeline security.
Security for oil and gas installations has long been a cause of concern in southwestern Pakistan where tribesmen often fight for a share of benefits from exploration.
Sui Southern operates in Sindh and neighbouring Baluchistan provinces and has more than 1.6 million customers.