The Colonial pipeline resumed operations on Wednesday, allowing petroleum supplies to begin reaching eastern US states five days after a cyber attack caused a shutdown that precipitated a run on fuel at petrol stations.

Colonial said it initiated a restart at roughly 5pm Eastern time, but cautioned that it would take “several days for the product delivery supply chain to return to normal”.

Jennifer Granholm, US energy secretary, confirmed the resumption of flows on Twitter, writing that she had spoken by phone with the chief executive of the Colonial Pipeline company.

The 5,500-mile pipeline system has capacity for 2.5m barrels a day of fuel, and is a critical artery delivering liquid fuels from oil refineries to states along the US eastern seaboard. It was shut last Friday after what the FBI said was a ransomware attack by a hacking group called DarkSide.

The shutdown pushed average US petrol prices above $3 a gallon on Wednesday, their highest level since 2014. Gasoline futures dropped about 1 per cent, to $2.14 a gallon, that evening after Colonial announced the pipeline’s restart.

Panic-buying in some locations of the US south-east led to shortages, with two-thirds of fuel stations in North Carolina reporting they were without petrol as motorists hoarded fuel, according to data provider GasBuddy.

“Now finally Americans can have some peace of mind that gasoline, diesel and jet fuel will begin flowing to affected areas once again,” said Patrick De Haan, head of petroleum analysis at GasBuddy.

Colonial pipeline hack leads to tightening in petrol supply. Map showing Colonial pipeline and refineries in the East Coast and Gulf Coast regions

However, returning the pipeline, which previously carried almost half of the fuel used on the east coast, to its previous level of service will take time. Colonial said some of its markets could experience “intermittent service interruptions during the start-up period”.

“Colonial will move as much gasoline, diesel, and jet fuel as is safely possible and will continue to do so until markets return to normal,” it added.

Jeff Lenard, vice-president of strategic industry initiatives at NACS, a convenience store trade association, warned that fuel travels at 3-5mph along the pipeline — or about 100 miles a day — meaning it will take some time for fuel shipped in the Gulf Coast to reach the north-east.

“I mean, it’s walking pace, so if you want to know how long it’ll take, you walk [from New York] to Houston. You’re going to need to wear some serious shoes,” said Lenard.

Richard Joswick, global head of oil analytics at S&P Global Platts, said gasoline stocks in the US north-east would likely fall to five-year lows as panic-buying had exacerbated the shortfall caused by the five-day pipeline outage.

A return to normal would take “a couple weeks at least” both for the east coast and for Gulf Coast refiners that had lost an outlet for their fuel over recent days, he said.

European fuel exporters had begun chartering vessels to increase shipments to the US, while the Biden administration loosened some rules in recent days to allow for more fuel made elsewhere in the country to be shipped or trucked to eastern states.