Access has been restored into the city of Wilmington, which had previously been cut off by floods from former Hurricane Florence, North Carolina’s top transportation official said.

Department of Transportation secretary James Trogdon said there is one major accessible route into the city of nearly 120,000 people.

Emergency workers were delivering truckloads of food and water to Wilmington as helicopters and boats pulled people from homes swamped by swollen rivers.

A car drives through floodwaters in Wilmington
A car drives through floodwaters in Wilmington (Chuck Burton/AP)

The deadly storm still had abundant rain and top winds around 25mph, and forecasters said it was expected to gradually pick up forward speed and complete a big turn towards the north east, which is in for as much as 6in of rain.

Flooding worries increased in West Virginia and Virginia, where roads were closed and power outages were on the rise. About 500,000 homes and businesses were in the dark.

In some places, the rain stopped after Florence moved on, and the sun peeked through, but North Carolina governor Roy Cooper urged residents evacuated from the hardest-hit areas to stay away because of closed roads and flooding.

“There’s too much going on,” he told a news conference.

The death toll climbed to at least 21 as authorities found the body of a one-year-old boy who was swept away after his mother drove into floodwaters and lost her grip on him while trying to get back to dry land, and an 88-year-old man’s car was swept off a road by floodwaters.

Florence was still massive, despite being downgraded to a post-tropical cyclone from a once-fearsome Category 4 hurricane.

Radar showed parts of the sprawling storm over six states, with North and South Carolina in the bullseye.

North Carolina emergency response officials tweeted that 23 truckloads of military meals and bottled water were delivered overnight to Wilmington, the state’s eighth-largest city.

One route into the city was reopened by midday on Monday, officials said.

Residents waited for hours outside stores and restaurants for water and other basic necessities.

County commission chairman Woody White said officials were planning for food and water to be flown into the coastal city, located on a peninsula with the rising Cape Fear River to the west and more water to the east.

Fears of what could be the worst flooding in the state’s history led officials to order tens of thousands to evacuate, although it was not clear how many had fled or even could.

North Carolina environmental regulators said several open-air manure pits at pig farms had failed and were spilling pollution.

The Department of Environmental Quality said the earthen dam at one lagoon in Duplin County had been breached. There were also seven reports of lagoon levels going over their tops or being inundated in Jones and Pender counties. State investigators will visit the sites when conditions allow.

The industrial-scale farms contain vast pits of animal faeces and urine that can pose a significant pollution threat if they are breached or inundated by floodwaters.