The Colonial Pipeline Company ships gasoline and jet fuel from the Gulf Coast of Texas to the populous East Coast through 5,500 miles (8,850 kilometres) of pipeline, serving 50 million consumers.
The company said it was the victim of a cybersecurity attack involving ransomware - attacks that encrypt computer systems and seek to extract payments from operators.
"This Declaration addresses the emergency conditions creating a need for immediate transportation of gasoline, diesel, jet fuel, and other refined petroleum products and provides necessary relief," the Department of Transportation said in a statement.
The emergency declaration allows for fuel to be transported by road to the affected states: Alabama, Arkansas, District of Columbia, Delaware, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, New Jersey, New York, North Carolina, Pennsylvania, South Carolina, Tennessee, Texas and Virginia.
The declaration also provides regulatory relief to commercial motor vehicle operations that are part of the emergency support efforts.
As we reported earlier, US fuel pipeline operator Colonial Pipeline temporarily halted all pipeline operations after a cyberattack, the company said in a statement late on Friday.
The company is a major US supplier of gasoline, diesel, jet fuel and other refined products. It transports around 45% of fuel supplies around the US east coast.