"The United States is offering our full assistance to Haiti and to others in the region. We will be providing both civilian and military disaster relief and humanitarian assistance and our prayers are with the people who have suffered, their families and their loved ones," she said in a speech in Hawaii.
USAid said it was sending disaster response teams made up of 72 personnel, six search-and-rescue dogs and up to 48 tonnes of rescue equipment.
"This is a tragic situation and we will work alongside the Haitian government to provide immediate assistance in the rescue effort," Rajiv Shah, USAid chief, told the AFP news agency.
Aid agencies have said speed is essential in helping survivors, although the first full assessments of the devastation and relief requirements are not likely to begin until first light on Wednesday.
"The immediate needs are medication and health care, drinking water, water purification filters and then basic needs such as shelter and hygiene kits – the basic necessities for living," Amy Knorr, Haiti programme manager for the charity World Vision, told Al Jazeera.
Elisabeth Byrs, the spokeswoman for the UN Office for the Co-ordination of Humanitarian Affairs, said: "The international newtwork of search and rescue teams has been alerted and are going to be deployed.
"We are also about to send an expert team, a disaster expert team," she told Al Jazeera from Geneva, Switzerland.
"The UN has already allocated a certain amount of money to kick-start the operation during the night from the UN response fund and we hope that donors will respond to any appeal we might make for the poor people of Haiti."
Paul Conneally, the Head of Media at the International Federation of Red Cross and Red Crescent Societies, told Al Jazeera said that his organisation already had people on the ground in Haiti.
"Nevertheless, even for those on the ground our ability to operate effectively is hugely constrained with massive logisitical problems caused by the earthquake," he said.
"We are focusing primarily on supporting life saving efforts, in terms of emergency efforts and search and rescue."
In Paris, Bernard Kouchner, the French foreign minister, said his country expressed its "complete solidarity" with Haiti, adding that a government crisis centre had begun working to mobilise and dispatch urgent aid to Port-au-Prince, the Haitian capital.
Canada, which hosts an 80,000-strong Haitian community, said it was "deeply concerned" with events unfolding in Haiti.
Lawrence Cannon, the Canadian foreign affairs minister said officials were "making contact with trusted humanitarian partners with a presence in the region to identify humanitarian needs resulting from this earthquake".
Immediate monetary assistance to Haiti has also been pledged by the Inter-American Development Bank (IADB), which said on Tuesday that it would provide $200,000 in emergency aid.
Luis Moreno, the bank's president, said that the funds would be used to provide food, water, medicine and temporary shelter for victims of the quake.
He also said the development bank, which focuses on Latin America and the Caribbean, could provide more funds to help with recovery and reconstruction.
The United Nations has also joined the relief effort, with former US president Bill Clinton, now a UN special envoy for Haiti, saying that his office and the rest of the UN system were monitoring information coming out of the country.
"We are committed to do whatever we can to assist the people of Haiti in their relief, rebuilding and recovery efforts," he said.
Already the poorest nation in the Americas, Haiti has been hit by a series of disasters recently and was battered by hurricanes in 2008.