SANTO DOMINGO, Jan. 13 (Xinhua) -- A major earthquake rocked Haiti on Tuesday, crushing thousands of buildings, including the presidential palace and the U.N. peacekeeping headquarters, and trapping untold numbers of people in the rubble of the capital city.

    The devastation from the magnitude-7.3 quake, the strongest ever recorded on the poor Caribbean island, was so complete that it seemed likely the death toll would run into the thousands, according to reports monitored here.

    The offices of the finance and public works ministries, the parliament building, a hospital and a cathedral were also among the many structures that were severely damaged or destroyed in Port-au-Prince, a city of about 2 million people.

    Much of the presidential palace pancaked on itself but President Rene Preval and his wife survived the earthquake.

    Preval told the Miami Herald that the toll from the quake was "unimaginable" and estimated that thousands had died.

    "Parliament has collapsed. The tax office has collapsed. Schools have collapsed. Hospitals have collapsed. There are a lot of schools that have a lot of dead people in them," the president told the newspaper.

    The earthquake struck at about 4:53 p.m. local time (2153 GMT) ,which was centered 15 km southwest of the capital city at a depth of 10 km, the U.S. Geological Survey (USGS) said.

    The USGS said the earthquake was followed by a tsunami seven minutes later and two aftershocks of 5.9-and 5.5-degrees respectively.

    Power supplies were cut off in affected areas and communications were scattered. Heavy casualties were feared although no official reports were yet available.

    According to the International Federation of the Red Cross, as many as 3 million people may have been affected by the massive earthquake.

    Red Cross spokesperson Paul Conneally said that at least one or two days more would be needed to determine a much clearer picture of the destruction.

    "There are massive, massive, massive challenges," Conneally said.

    The Associated Press reported that the Port-au-Prince airport had opened but that the main road connecting it to the capital remained impassable. Other roads had been torn apart in the quake or were blocked by debris, making it more difficult to transport food, fresh water and first aid supplies and hospitals were overwhelmed by the injured.

    The head of the U.N. mission in Haiti, Hedi Annabi, apparently was killed in the earthquake, said French Foreign Minister Bernard Kouchner.

    "It would appear that everyone who was in the building, including my friend Hedi Annabi, the United Nations' Secretary General's special envoy, and everyone with him and around him are dead," Kouchner told RTL radio on Wednesday.

    A senior U.N. official said Wednesday that five people have been confirmed killed in the collapse of the organization's headquarters in Haiti.

    Eight Chinese U.N. peacekeepers were buried in the rubble of the earthquake, according to a statement released by the State Council. There are 125 Chinese in Haiti as part of the U.N. stabilization mission on the island nation.

    Additionally, at least 11 Brazilian U.N. peacekeepers were killed in the earthquake, updating the previous account of four, the Brazilian military said Wednesday.

    Brazilian Defense Minister Nelson Jobin and General Enzo Martins Peri were headed to the Haitian capital to get a full accounting of Brazil's peacekeepers in the Caribbean country, said military spokesman General Carlos Alberto Barcellos.

    With 1,266 soldiers, Brazil contributes the most to the 9,000-strong multi-national peacekeeping mission.

    The earthquake was also felt in the Dominican Republic, which shares the Espanola Island with Haiti, and in eastern Cuba but no major damage was reported in either place. The Dominican Republic has asked for assistance to Haiti.

    "The information we have is that the situation in Haiti is difficult, so we ask Latin America and all the world to help our neighbor," said Dominican Republic presidential office spokesman Frafael Nunez.

    U.N. Secretary General Ban Ki-moon said the earthquake has had a devastating impact on Port-au-Prince and called for major disaster relief efforts in Haiti. He also plans to visit Haiti as soon as possible.

    U.S. President Barack Obama has said his country was ready to send in humanitarian aid. He also vowed a 'swift, coordinated and aggressive' effort in Haiti.

    "This is a time when we are reminded of the common humanity that we all share," Obama said at the White House with Vice President Joseph Biden at his side.

    The United States and other nations from Iceland to Venezuela began organizing aid efforts, alerting search teams and gathering supplies that will be badly needed in the Western Hemisphere's poorest country.

    Three U.S. rescue teams leaving for the Port-au-Prince will depart on Wednesday, said the U.S. State Department spokesman Philip Crowley.

    The European Union has announced it will provide three million (4.36 million dollars) in emergency disaster relief, said a commission spokesman on humanitarian aid matters.

    Brazil also announced that it was sending 10 million dollars in immediate aid, according to reports.

    The UN's World Food Program (WFP) said it would respond swiftly with some 15,000 tons of food supplies in Haiti.

    "We have already launched an emergency operation," said WFP official Charles Vincent.

    Many other countries are also offering their aid. French President Nicolas Sarkozy said France would send planes with rescuers and humanitarian relief goods to the disaster-hit nation.

    Most of Haiti's 9 million people are desperately poor, and after years of political instability the country has no real construction standards.