Port-au-Prince, Haiti (CNN) -- "Port-au-Prince is flattened" after a 7.0-magnitude earthquake struck the Haitian capital, Haiti's consul general to the United Nations said Wednesday.
"More than 100,000 are dead," Felix Augustin told reporters.
The hospitals are gone, he added, and medical supplies and heavy equipment are desperately needed.
The Haitian prime minister said Wednesday several hundred thousand people may have died in the powerful earthquake.
"I hope that is not true, because I hope the people had the time to get out," Jean-Max Bellerive told CNN.
"Because we have so [many] people on the streets right now, we don't know exactly where they were living. But so many, so many buildings, so many neighborhoods totally destroyed, and some neighborhoods we don't even see people."
Bellerive told CNN's Gary Tuchman all of Port-au-Prince is either damaged or destroyed. He said the population is calm, and authorities are working to determine the scope of the destruction and reach a better conclusion on how many people were killed or injured.
"With maturity, people are trying to take care of themselves in some quiet places. People are trying to help each other on the streets," he said.
Hear the prime minister describe the situation Video
U.S. Gen. Douglas Fraser said he expects "there will be a significant loss of life." French President Nicolas Sarkozy said "there's every reason to fear that this earthquake has caused a large number of casualties."
Earlier, Haiti's first lady, Elisabeth Debrosse Delatour, reported that "most of Port-au-Prince is destroyed," the Haitian ambassador to the United States, Raymond Joseph, said. He called the quake a "major catastrophe."
U.N. Secretary-General Ban Ki-moon spoke of the collapse of "basic services such as water and electricity."
About 3 million people -- one-third of Haiti's population -- were affected by the quake, the Red Cross estimated. About 10 million people felt shaking from the earthquake, including 2 million who felt severe trembling, the U.S. Geological Survey estimated.
President Obama announced a "swift, coordinated and aggressive" U.S. response.
"The reports and images that we've seen of collapsed hospitals, crumbled homes and men and women carrying their injured neighbors through the streets are truly heart-wrenching," Obama said.
Aid groups scrambled to help.
None of the three aid centers run by Doctors Without Borders is operable, the group said, and the organization is focusing on re-establishing surgical capacity so it can deal with the crushed limbs and head wounds it is seeing.
Authorities braced for civil disturbances.
Edmond Mulet, the U.N. assistant secretary-general for peacekeeping operations, told CNN that the National Penitentiary collapsed and the inmates escaped, prompting worries about looting by escapees.
Built in 1915, the prison was overcrowded. Enlarged to a total capacity of 1,200, it held 3,908 inmates in December, the U.S. State Department has said.
The powerful 7.0-magnitude earthquake struck shortly before 5 p.m. Tuesday, centered about 10 miles (15 kilometers) southwest of Port-au-Prince, the U.S. Geological Survey reported. It could be felt strongly in eastern Cuba, more than 200 miles away.
The earthquake's power matched that of several nuclear bombs, said Roger Searle, a professor of geophysics in the Earth Sciences Department at Durham University in England. He said the combination of its magnitude and geographical shallowness made it particularly dangerous.
The earthquake sheared huge slabs of concrete off structures and pancaked scores of them, trapping people inside those buildings, and knocking down phone and power lines.
Many buildings that remained standing were left open to the elements, pictures from the scene showed, and citizens were dusty from the concrete and in some cases bloody from their injuries.
"One woman, I could only see her head and the rest of her body was trapped under a block wall," said Jonathan de la Durantaye, who drove through Port-au-Prince after the quake. "I think she was dead. She had blood coming out of her eyes and nose and ears."
CNN's Anderson Cooper, viewing Port-au-Prince from a helicopter, called the sight of the destroyed buildings in the quake-devastated city "incredibly shocking" and "eerie."
He said many people are "just kind of standing around on the streets, not really sure what to do or where to go. And for many, there is nowhere to go."
Ban said the U.N. headquarters at the Christopher Hotel collapsed in the quake, and that people were still trapped inside. He said possibly 100 or 150 people were in the building around the time the quake struck. He said the chief of the U.N. mission in Haiti and a deputy special representative had not been accounted for.
At least 15 peacekeepers were reported to have died. The Brazilian Army said 11 of its soldiers were killed, while state-run media in Jordan reported the deaths of three Jordanian peacekeepers. The Argentine military confirmed the death of one peacekeeper from Argentina.
Joseph Serge Miot, the archbishop of Port-au-Prince, died in the quake, according to the official Vatican newspaper.
A U.S. Coast Guard helicopter evacuated four critically injured U.S. Embassy staff to the Naval Station Guantanamo, Cuba, hospital for further treatment.
Cheryl Mills, counselor to the secretary of state and an expert on Haiti policy at the U.S. State Department, said about 80 embassy spouses, children and non-essential personnel planned to leave Wednesday afternoon.
Obama urged Americans trying to locate family members in Haiti to telephone the State Department at 888-407-4747.
Haiti's main airport appeared to be operable, which should enable foreign aid to start flowing into the country, and U.S. Embassy staff at the airport said the tower and the lights were working, State Department Spokesman P.J. Crowley said Wednesday.
Rajiv Shah, administrator of the U.S. Agency for International Development, will be the U.S. government's unified disaster coordinator, Obama said. Shah told CNN that teams have been working around the clock "to make sure the U.S. mounts an effective response in supporting saving lives, which is the president's absolute top priority for this first period of 72 hours when we search and save as many lives as we can."
Many countries and agencies across the globe geared up to help Haiti. A 50-member Chinese rescue team planned to deploy, Xinhua news agency said, and Ban said the U.N. plans to release $10 million in aid immediately.
The U.S. military is working to get ground and air assessments of the damage.
U.S. officials say the USNS Comfort, a Navy hospital ship in port in Baltimore, has begun to recall its crew and is standing by for orders to head to Haiti. All East-coast based Navy ships have been alerted for standby, the officials said.
Two Coast Guard C-130 airplanes were doing damage assessments and searches, and helicopters were deployed to the scene.
I had no idea the scale of the tragedy was so staggering. Up to a third of the population may have been affected according to the slideshow; it's difficult if not impossible for me to imagine what it must be like.