Washington, USA: Several east coast US states declared a state of emergency on Tuesday as gas stations began to run out of gasoline, five days after a cyberattack brought down the key Colonial pipeline.

Despite assurances from President Joe Biden's administration that the pipeline, which provides almost half the gas to the eastern seaboard, would be up and running within days, panicked drivers continued to top up their tanks.

Declaring a state of emergency allows state governments to activate the National Guard as needed, and helps streamline cooperation between state and local officials.

Where are gas stations running out of gas?

In the Georgia metropolis of Atlanta, some 30% of gas stations had run dry, with a similar number in Raleigh, North Carolina, according to the tracking firm GasBuddy.

By 4 p.m. EST (20:00 UTC) almost 8% of gas stations throughout the state of Virginia had run out of gas, while in Florida close to 3% were empty, CNN reported.

Granholm said that there was not a supply shortage, but rather a "crunch" in some states that are particularly reliant on the Colonial pipeline.

Georgia lifted sales tax on gas until Saturday to help consumers while the federal government temporarily loosened certain environmental and working hours regulations to smooth out the problems.

What caused the pipeline shutdown?

Colonial said it was hit by a ransomware attack on Friday;  hackers typically lock up computer systems by encrypting data and then demand a large ransom to decrypt it.

The FBI said on Monday that it suspected the professional cybercriminal group DarkSide to be behind the attack.

The attack highlighted the vulnerability of US infrastructure to cybercriminals.

Ohio Senator Rob Portman told a Senate hearing on cybersecurity threats on Tuesday that the strike on Colonial was potentially "the most substantial and damaging attack on US critical infrastructure ever."