US motorists have been urged to not hoard fuel as supplies tighten due to a major pipeline remaining shut after a cyber-attack.
Some drivers in the south east were seen stocking up as petrol stations began running dry and prices rose.
The average price for petrol was the highest on Tuesday since November 2014, at $2.98 (£2.11) per gallon, the American Automobile Association said.
North Carolina, Virginia and Florida have declared a state of emergency.
Ms Granholm said there was not a shortage but a supply “crunch” in North Carolina, South Carolina, Tennessee, Georgia and southern Virginia, regions that typically rely on Colonial for fuel.
A ransomware cyber-attack on Friday forced Colonial Pipeline to shut down the main part of its network.
The operator has forecast that it will not substantially restore operations of the 5,500-mile (8,900km) pipeline network that supplies nearly half of the East Coast’s fuel until the end of the week.
The FBI has accused a criminal gang called DarkSide of the ransomware attack.
The gang is believed to be based in Russia or Eastern Europe and avoids targeting computers that use languages from former Soviet republics, cyber experts said.
Ransomware is a type of malware designed to lock computers by encrypting data and demanding payment to regain access.
Russia’s embassy in the US rejected speculation that the country’s government was behind the attack.
If the general public or politicians ever needed proof of how devastating cyber-attacks can be, this hack will more than suffice: chaos at the pumps, states of emergency declared and the White House calling for calm.
And this is just the stuff we’re being told about.
In Colonial Pipeline’s latest press update, we’re given hints about the mayhem inside the company.
With high-tech sensors and safety systems taken offline, the firm says it’s hired dozens of staff to walk or drive the 5,000-mile length of the pipeline every day.
It’s also deployed helicopters to check on the pipes and a growing fleet of delivery trucks.
Colonial says this is a separate problem, but tellingly it has now blocked all traffic from outside of the US.
Even the hackers themselves seem surprised by the damage they’ve caused.
According to new research from cyber-security company FireEye, the hackers known as Darkside launched global crime spree in August last year, raking in millions from organisations in more than 15 countries.
But this hack seems like it may have crossed some sort of line even for these hardened criminals. The true test of their morals, though, will depend on whether or not they will continue the extort the company or help it recover.
More than 7% of petrol stations in Virginia and 5% in North Carolina were out of fuel on Tuesday as demand jumped 20%, tracking firm GasBuddy said.
On Tuesday, the government stepped in to issue an emergency fuel waiver lasting one week, designed to help alleviate any shortages.
The Environmental Protection Agency (EPA) said the move, which relaxes some rules usually applied to fuel, would run until 18 May in Pennsylvania, Virginia, Maryland, and Washington DC.
In addition, Georgia suspended sales tax on petrol until Saturday.
On Monday North Carolina declared a state of emergency and temporarily suspended vehicle fuel regulations “to ensure adequate fuel supply supplies throughout the state”.
While the pipeline outage is having short-term consequences in some regions, some experts believe the longer term impact will be small.
“Markets will go crazy, but two weeks later no one knows it happened,” said Chuck Watson, director of research at Enki, which studies the economic effects of natural and other disasters.
Fuel prices were expected to rise with the start of the summer driving season, although the US Energy Information Administration said on Tuesday that the ongoing effects of the Covid-19 pandemic would “significantly affect petroleum markets in the summer of 2021”.
The pipeline shutdown contributed to the rise in fuel prices, the AAA said.
“We might see the delivery challenges due to the attack add a few cents to the expected increase in the national average,” a spokesperson added.