Colonial Pipeline, the major US pipeline network forced offline by a cyber attack, has begun to reopen, the company said on Wednesday, however, cautioned that it will take “several days” for fuel supplies to return to normal.

Colonial Pipeline said it “initiated the restart of pipeline operations today at approximately 5 pm ET,” but some markets “may experience, or continue to experience, intermittent service interruptions during the start-up period.”

The shutting down of one of the nation’s largest oil transporter led to exposing vulnerabilities in America’s infrastructure and sparking gas panic buying across the southeast.

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“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,” the company said.

US President Joe Biden earlier Wednesday tried to reassure Americans, saying his officials had been “in very, very close contact” with the company.

The Transportation Department and Environmental Protection Agency (EPA) have eased regulations on transporting fuel and temporarily waived clean air rules throughout the affected states to try to ease the supply crunch.

Colonial Pipeline operates the largest US fuel conduit system in the United States, which sends gasoline and jet fuel from the Gulf Coast of Texas to the populous east coast through 5,500 miles (8,850 kilometres) of ducts that serve 50 million consumers.

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The restoration of supplies will come as a relief to motorists who drove a wave of panic buying that caused thousands of stations to run dry, according to gas price tracking site GasBuddy — which itself was crashing under the volume of new users.

US average gasoline prices rose $3 a gallon for the first time since November 2014, according to the American Automobile Association (AAA).

Transportation Secretary Pete Buttigieg on Wednesday urged consumers to remain calm.

“We recognize the concern that is out there, and that’s why we haven’t wasted any time to get into action,” he told reporters at the White House. “Hoarding does not make things better.”

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The FBI blamed the shadowy DarkSide group for the ransomware attack, in which hackers freeze corporate IT systems and then demand a huge payment to release it.

But according to a report in The Washington Post on Wednesday, Colonial Pipeline has no plans to pay the ransom.

Instead, it is working with a cybersecurity firm to rebuild its systems or restore them from backups, the report said, citing people familiar with the matter.