The politically unstable country was already the poorest in the western hemisphere before the quake, and with many buildings unable to withstand the tremors, the situation has been made much worse.
Haiti's near neighbour, the United States, has offered one of the largest contributions, with President Barack Obama pledging $US100 million ($A107.6 million) in immediate aid.
Washington is also sending rescue teams, ships, helicopters, planes, a floating hospital, emergency supplies and more then 5,000 ground troops.
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But other countries have also been quick to respond.
US State Department spokesman P.J. Crowley said on Thursday that eight international search-and-rescue teams were already on the ground in Port-au-Prince comprising about 260 personnel.
Apart from the US, there were also staff in place from Iceland, Spain and Chile, he said, adding they had already helped free people from the ruins.
"Obviously this is still a very growing list, but our estimate is that at least 30 countries have meaningful assistance that has already reached Haiti or is en route." he said.
"So not only is the United States' commitment to Haiti growing, but also the international commitment as well."
UN assistance
UN Chief Ban Ki-moon announced earlier that relief workers from China, the Dominican Republic, France and Venezuela had also joined the huge operation.
He added that $US10 million ($A10.7 million) would be released immediately from emergency funds.
The UN World Food Program, which was already working in Haiti, is distributing high energy biscuits and airlifting in 86 tons of food from El Salvador, with thousands more tons to come.
The UN is also making an emergency appeal for additional funds from member states.
The Australian government's AusAID emergency relief program is giving $A10 million in emergency humanitarian relief and reconstruction assistance.
The European Union and its members have pledged millions of dollars, as well as sending people and equipment.
Charities and aid agencies
International charities and aid agencies are also sending assistance to Haiti, backed by donations from ordinary citizens.
The International Red Cross already has staff there, and is sending two planes from Geneva carrying medical equipment and doctors, as well as specialists in reuniting families separated by disaster.
Médecins Sans Frontières teams were also already in Haiti working on medical projects and are now helping to treat the injured.
Paul McPhun from MSF says all of the organisations buildings were destroyed by the quake and the extent of the injuries is overwhelming medical staff.
“The reality of what we're seeing is severe traumas, head wounds, crushed limbs, severe problems that can not be dealt with, with the level of medical care that we currently have available with no infrastructure to support it.” he said.
Oxfam Australia says the charity has 100 staff on the ground responding with public health, water, and sanitation services to prevent the spread of disease.
Save The Children Australia says it's released $A150,000 from its newly created Children's Emergency fund, which will be directed immediately to the most vulnerable children and their families in Haiti.
But everyone sending aid knows it's only the start of the relief effort, with years of help likely to be needed to rebuild the country.
Go to our special How you can help page for details of how to donate.
