The FBI was called in after two power plants in North Carolina were shot down, leaving tens of thousands without power.
Throughout Moore County, businesses, stores and restaurants were forced to close, traffic lights were turned off and emergency shelters were set up following the attack.
A state of emergency was declared on Tuesday and schools will be closed for the second consecutive day.
The statement includes a countywide nighttime curfew through at least Friday.
A total of 38,000 households are left without electricity due to freezing night temperatures. At the peak, 45,000 were powerless.
North Carolina Governor Roy Cooper warned of a “new level of threat” posed by the incident and called for better protection of critical infrastructure, including the power grid.
“Protecting critical infrastructure such as our energy system must be a top priority,” he said. “This kind of thing can’t happen.”
When asked if the attack was being investigated as an act of domestic terrorism, Cooper said “investigators are leaving no stone unturned.”
Police said the shooting was committed by someone with “criminal intent”.
Their comment came after speculation surfaced online that the attack was a protest against a drag act scheduled for Saturday.
Organizers of the show at Southern Pines’ Sunrise Theater said far-right activists had been trying to shut down the show for weeks, but police said they found no evidence to support the theory.
Federal agencies including the FBI and the US Department of Energy are investigating the shootings, along with local and state law enforcement agencies.
So far no one has suggested a motive and no arrests have been made.
US President Joe Biden was briefed on the incident, which occurred on Saturday, the White House said.
Moore County is located approximately 60 miles (95 km) southwest of the state capital of Raleigh.
Sheriff Ronnie Fields said the perpetrators “knew exactly what they were doing to … cause the disruption they did.”
