"What happens is that we rescue some people and then we find out there are still more who need it", he said.
Operations at the ports of Wilmington, Charleston, South Carolina, and Norfolk in Virginia, which together handled 23 per cent of East Coast imports in 2017, have been disrupted by the storm.
And while Florence was downgraded to a tropical storm Friday afternoon, meteorologists predict heavy rain - up to 2 feet of rain when all is said and done - will continue into the weekend.
At the time, the storm carried winds of about 90 miles per hour (145 km/h), making it a Category 1 storm, but that ranking belies the hurricane's massive clouds and the downpour it is visiting on the coastline, with some areas already drenched in 30 inches (76 centimeters) of rain.
Florence was seen as a major test for the Federal Emergency Management Agency, which was heavily criticized as slow and unprepared past year for Hurricane Maria in Puerto Rico, where the storm was blamed for almost 3,000 deaths in the desperate aftermath. "We are stuck in the attic". "The storm is wreaking havoc on our state".
More than 12,000 people were in shelters in North Carolina and 400 in Virginia, where the forecast was less dire.
President Donald Trump is preparing to travel to areas affected by the storm next week.