Updated

The expected high winds and slow movement of Hurricane Florence as it comes ashore will make rescue efforts challenging in the flooded areas, top Pentagon leaders said Thursday as the massive storm edged into the Carolinas.

Air Force Gen. Terrence J. O'Shaughnessy, head of U.S. Northern Command, said that while search and rescue is a top priority, the weather may prevent rescuers from getting in during the hours immediately after the storm hits.

"This particular storm I think is going to be challenging," O'Shaughnessy told reporters during a Pentagon briefing. "Because of the slow-moving nature of the storm, it could very well stay with high winds, inclement weather for a long period of time, which is going to mean that any rescue effort is going to take time."

He said it's not clear how many people refused to evacuate and have hunkered down in their homes or shelters. But getting to any of those in need will be difficult in the early stages of the storm.

According to O-Shaughnessy, there are about 7,000 U.S. military forces, including 4,000 National Guard and 3,000 active duty, currently in place and ready to respond to the storm, along with ships, helicopters, high-wheeled vehicles and other equipment. And, thousands of additional troops have been ordered to prepare to deploy if needed.

He warned that while local National Guard forces are well-positioned to respond to search and rescue needs, "the magnitude of the storm may exceed their capability." If that happens, he said the active duty troops and Coast Guard will be ready "at a moment's notice."

The military, he said, has "quite literally surrounded the expected affected area" with forces at sea ready to chase the storm inward, and others ready to drive into the flooded zones in heavy, high-wheeled trucks from the south and west. About 240 high-water vehicles are available, and O-Shaughnessy said the military has been moving the trucks to keep them as close to the storm as possible, so they may be able to begin search and rescue more quickly, if the ships can't get ashore fast enough.

The Navy's amphibious assault ship USS Kearsarge and the amphibious transport ship USS Arlington are ready to respond, with about 800 Marines from the 22nd Marine Expeditionary Unit aboard. According to Navy Lt. Jamie Seibel, the ships already have the resources and supplies they need, including a fleet surgical team, engineers and damage assessment personnel, as well as heavy and medium lift helicopters, search and rescue aircraft and smaller ship-to-shore landing craft.

A number of military bases in Virginia, Alabama and the Carolinas are being used as staging bases for aid. Dozens of helicopters and trucks have been stationed at those bases and further out in Kentucky, Georgia, Texas, Arizona, New York, and Delaware.

Federal and state officials have often struggled with gaps in emergency response during previous storms, because they were waiting for local authorities to make official requests for aid.

O'Shaughnessy and Kenneth Rapuano, the assistant defense secretary for homeland defense, said the Pentagon has pre-approved any expected requests for life-saving assistances the states may make. Marines riding out the hurricane at Camp Lejeune will be able to move quickly to support local authorities and help citizens nearby.