An estimated 40,000 people in northern South Australia are without supply with APA Group revealing that bottled gas had been sent to hospitals in the cut-off cities of Whyalla and Port Pirie.

Epic CEO Clive D'Cruz said the pipeline incident took place in an isolated region near Gladstone in South Australia's mid-north.

Epic said the area was now secured with road closures occurring in Caltowie, Gladstone and Jamestown.

"We have despatched our staff to the site to begin a thorough assessment and we are working closely with emergency services," D'Cruz said today.

"At this stage it would be premature to speculate on what may have occurred. Closing this section of the pipeline is very likely to have an impact on Whyalla."

Gas supplies are not expected to be restored until the end of next week with Whyalla Mayor Jim Pollock already worried about the losses faced by businesses.

"Issues happen, accidents happen but five days [without gas] is an extremely long time," he told the ABC.

APA has opened up a hotline, 1800 898 220, to provide updates.