At least 1.4 million people need urgent assistance, more than 300 schools have been damaged while crops and food reserves have been destroyed, he said.
"A massive response is required," Ban told reporters.
The United Nations has launched a $120 million flash appeal to cover the needs in Haiti for the next three months.
"Some towns and villages have been almost wiped off the map," he said.
"These numbers and needs are growing as more affected areas are reached."
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Haitian officials said Monday that the death toll from the hurricane had risen to 372, but hundreds more are feared dead as rescue workers reach more areas.
"I call on the international community to show solidarity and generosity -- and to work together effectively in responding to this emergency," Ban said.
Matthew was downgraded Sunday to a post-tropical cyclone.
It crashed ashore on Haiti's southern coast on October 4 as a monster Category 4 storm, packing winds of 145 miles (230 kilometers) per hour.
UN aid chief Stephen O'Brien said the hurricane had triggered the worst humanitarian crisis in Haiti since the 2010 earthquake.
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Matthew hit when Haitians were already struggling with a worsening cholera outbreak, blamed on UN peacekeepers, that has already killed 10,000 people.
The United Nations is working on a financial package to compensate the families of cholera victims and help build sound water and sanitation systems on the Caribbean island.
The UN's children's agency said 100,000 children will be missing out on learning after their schools were damaged or converted into emergency shelters.
UNICEF is working to set up temporary classrooms and deliver new school supplies.
