Every truck moving, full or empty, is mobbed by survivors desperate for food and clean water, according to a BBC correspondent.
Many residents have been forced to take shelter on rooftops.
The confirmed death toll has reached 1,013 in Gonaives, with about 1,200 more missing.
The UN World Food Programme estimates 175,000 people are without food, water and electricity.
UN helicopters have already brought emergency supplies to Gonaives but the trucks are having trouble getting through the flood waters.