A day after the great Haiti earthquake, the country's president, Rene Preval, speculated that 30-50,000 people may have died -- though officials conceded there was no real way to make an estimate amid the chaos in the poorest country in the Western Hemisphere.
Stunned Haitians piled their dead on the crumbling streets of the capital, Port-au-Prince, and Preval reported stepping over dead bodies.
"Dead bodies are everywhere," said Frederic Dupoux, a resident of the city, in a Twitter feed. "I haven't seen one ambulance or any professional medical care anywhere in Port-au-Prince."
The quake struck late Tuesday afternoon, its epicenter just 10 miles from the densely-populated capital. It had a magnitude of 7.0, making it the worst earthquake to hit Haiti in 240 years.
While specifics on the number of casualties from the earthquake remained unclear, early reports point to heavy and widespread damage.
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Two nurses from Chicago Children's Memorial Hospital happened to be working at a clinic in the town of Gramothe when the earthquake struck. They sent a message early Wednesday morning:
"At least 100 horrifically injured patients were ministered to by this group of 23 as they came to the rescue of two doctors and just a few nurses left to handle the masses of wounded," they wrote.
"Words cannot express our thanks for your prayers tonight. Please continue to pray for Haiti."
"Port-au-Prince is a very mountainous city," said Magalie Boyer, an aid worker for World Vision Haiti, in a telelphone interview with ABC News. "So a lot of people have gathered up their belongings and are carrying them on their heads, carrying them in baskets, carrying them on their backs and just heading up the mountains hoping to find safer ground."
Another aid worker, talking to ABC News on the condition he not be identified, said it was likely that several thousand people had died in the disaster, but that early claims by government officials -- of more than 100,000 dead -- were overblown.
The aid worker said there are not whole sections of Port-au-Prince that have been devastated, though there are pockets. He said some parts of the city have power, some food seems to be available, and traffic is moving, albeit slowly.
This afternoon the United Nations reported that of the 9,000 uniformed peacekeeping personnel it had stationed in Haiti, 16 had died.
Tens of thousands of people are estimated to have lost their homes when poorly-constructed buildings collapsed in the earthquake.
"A school near here collapsed totally," said Ken Michel, a resident of Petionville, a hilly suburb of Port-au-Prince where many diplomats and aid workers live. He surveyed the damage and said, "We don't know if there were any children inside."
Mark Marek, the head of programs for the American Red Cross in Haiti, told ABC News via Skype that much of its rescue equipment would have to be delivered by hand because "the roads are blocked and equipment needs to get into houses that are built on steep inclines and mountains."
Another aid worker e-mailed home, "I myself am an earthquake veteran of the Philippines and Los Angeles, and this was the worst quake I have ever experienced. The Embassy, made of solid stone and steel, bounced and shimmied like an old jalopy driving on a potholed road."
President Obama said the United States government would offer "swift, coordinated, and aggressive" aid to the estimated three million people caught in the disaster.
"This is a time when we're reminded of the common humanity that we all share," Obama said. "With just a few hundred miles of ocean between us and a long history that binds us together, Haitians are our neighbors in the Americas and here at home."
Secretary of State Hillary Clinton joined in: "It is Biblical, the tragedy that continues to daunt Haiti and the Haitian people. It is so tragic." Clinton was on a trip to talk with leaders of nations in the Pacific Rim, but she cut it short to return to Washington.
Aftershocks continued today, though they were diminishing in strength and frequency.
A radio host named Carel Pedre described what he saw via Twitter, writing, "1st After Shock Of The Day!!! Haiti is still shaking!! HELP!!"
Pedre broke into tears during a phone interview. "I've not had any contact from my mother and my brother and I wonder about what's going to happen and I'm scared," he said.
Another man in Port-au-Prince, Richard Morse, said, "Everyone slept outside last night. People are afraid of remaining inside buildings. As I walked the streets I see bodies.
"People are calm, trying to help each other," he said. "Others are visiting people to see if they are OK. Some are digging bodies out of buildings."
The control tower at the country's main airport is said to have collapsed, hindering rescue efforts, but the runways were usable and the U.S. Air Force sent in equipment to provide air traffic control for relief planes.
Commercial flights were canceled, but American Airlines told ABC News it sent "a couple" of American Eagle commuter jets from San Juan, Puerto Rico, carrying supplies for airline employees.
Haitian-born rap star Wyclef Jean, arguably the most recognizable Haitian in the world, has been urging his fans to donate money to relief efforts through his foundation, Yele Haiti. The 37-year old star said he is on his way to Haiti, a country for which he was made roving ambassador in 2007.
"Haiti has suffered a natural disaster of unprecedented proportions…unlike anything the country has ever experienced," he wrote on his Web site.
The White House said Americans trying to locate family members in Haiti can call the State Department at 888-407-4747. The president said that while Americans may be facing financial trouble at home, those who wanted to donate money to the rescue effort could go to www.whitehouse.gov for more information on how to contribute.
According to the U.N., collapsed buildings include the national penitentiary, where prisoners have escaped, the presidential palace, the Parliament Building, the National Cathedral and at least four other ministry buildings including the finance ministry.
Obama said search-and-rescue teams from Florida, California and Virginia would arrive in Haiti today and tomorrow, with more teams being prepared.
"The rescue and recovery effort will be complex and challenging," he said. "The first hours and days are absolutely critical to saving lives and avoiding greater tragedy."
The president has designated Dr. Raj Shah, the administrator of the U.S. Agency for International Development, as disaster coordinator for the U.S. response to the Haitian earthquake.
Private agencies, such as the American Red Cross, Doctors Without Borders and Food for the Poor were mobilizing relief efforts as well. The United Nations Foundation, founded by Ted Turner, pledged $1 million to the U.N.'s Central Emergency Response Fund (CERF). The Red Cross also said it was releasing $1 million for immediate relief, though it added that its office in Port-au-Prince had been destroyed.
By this evening, two Coast Guard cutters, the Forward and the Mohawk, had arrived at Port-au-Prince. Each has a helicopter flight deck, satellite communications equipment, and the ability to provide coordination to military aircraft in the area. Two other cutters, the Tahoma and the Valiant, were on the way.
Two Coast Guard C-130 cargo planes were sent to evacuate U.S. embassy personnel to Santo Domingo in the neighboring Dominican Republic.
"It is a catastrophe, it is terrible. The access to Port-au-Prince now is impossible by car," said Louis St. Germain, a pastor who runs an orphanage in the town of Les Cayes. "So the whole city is in panic."
ABC News' Dan Harris, Kate Snow, Martha Raddatz, Suzan Clarke, Luis Martinez, Dennis Powell, Matt Hosford and Kirit Radia contributed reporting for this story.