Buildings and infrastructure in Port-au-Prince suffered extensive damage, while basic services, including water and electricity are near the brink of collapse. The full extent of casualties, which could number in the hundreds, is still unknown, Mr. Ban told reporters in New York.
"There is no doubt that we are facing a major humanitarian emergency and that a major relief effort will be required," he said.
Expressing gratitude to nations rushing aid to the earthquake's victims, he called for the world to "come to Haiti's aid in this hour of need."
The UN, he said, is also mobilizing an emergency response team to help coordinate humanitarian relief efforts and is expected to be on the ground shortly.
Many of UN personnel serving in the country - including Hédi Annabi, the Secretary-General's Special Representative - are still unaccounted for, Mr. Ban said, with the UN Headquarters in the Christopher Hotel having collapsed in the tremors.
"Many people are still trapped inside," the Secretary-General - who has been in close consultation with the Governments of Haiti, the United States and others - noted.
Troops, mostly from Brazil, serving with the UN Stabilization Mission in Haiti (MINUSTAH) have been working through the night to reach those trapped under the rubble, and several badly injured people have been rescued and transported to the mission's logistics base which remains intact.
Alain Le Roy, Under-Secretary-General for Peacekeeping, told journalists today that fewer than 10 UN staff were pulled out of the collapsed Christopher Hotel, with some of them confirmed to have died.
The Montana Hotel, where some UN personnel lived, also collapsed, he said.
UN Development Programme (UNDP) Administrator Helen Clark told reporters that some 38 members of her staff are unaccounted for.
The Secretary-General announced today that he will dispatch Edmond Mulet, his former Special Representative to Haiti and current Assistant-Secretary-General for Peacekeeping Operations, to the country, and that the UN Central Emergency Relief Fund (CERF) is releasing $10 million immediately.
"The first priority is search and rescue," with teams from the US, China, France, the Dominican Republic and other nations on their way to Haiti, Under-Secretary-General for Humanitarian Affairs John Holmes told reporters today.
The UN, he said, will launch a flash appeal to kickstart what "will certainly be a major operation and a major relief effort."
MINUSTAH was set up in 2004 and currently has more than 9,000 military and police personnel and nearly 2,000 civilian staff. Some 3,000 of the mission's troops and police are in and around Port-au-Prince, and will help to maintain order and assist in relief efforts. They have also started to clear some of the capital's main roads to allow aid and rescuers to reach those in need.