Washington's mayor Muriel Bowser announced the state of emergency as Hurricane Florence if moving in the direction of the US East Coast, threatening torrential rain and flooding in the capital region.
The declaration said that the health, safety and welfare of Washington, DC's residents require "emergency protective actions" because the storm is expected to have "serious widespread effects" throughout the region.
Meanwhile, the state of South Carolina has mobilized about 1,600 National Guard members in preparation of Hurricane Florence, the US Department of Defense said in a news release on Tuesday.
"As South Carolina residents and emergency responders prepare for Hurricane Florence, the South Carolina National Guard has mobilized about 1,600 soldiers and airmen to prepare, respond and participate in advance of the major hurricane projected to make landfall near the Carolinas," the release said.
Hurricane Florence is expected to make landfall somewhere along the southeastern United States, likely near the border between the Carolinas, early Friday.
The storm weakened slightly, but is expected to regain strength by the end of the day, and will be a Category 4 or 5 when it reaches the US coast.