Haitian President Rene Preval on Wednesday pleaded for assistance after Tuesday's devastating 7.3-magnitude earthquake brought about "unbelievable catastrophe" to his country.

"Parliament has collapsed. The tax office has collapsed. Schools have collapsed. Hospitals have collapsed," he told reporters in a street in Port-au-Prince, the capital of the island state.

"There are a lot of schools that have a lot of dead people in them," said the saddened president, who had been stepping over dead bodies piled in the streets and amid cries of people, who had been injured or bereaved of their beloved ones.

Preval's presidential residence, a domed white building, was also flattened by the quake. Fortunately, the president was not injured.

The temblor, the strongest ever recorded in the region in more than 200 years, may lead to tremendous casualties although it is too early to determine the exact number.

Up to 100,000 people might have died in the quake, said Mauricio Bustamante, operation coordinator of the International Federation of Red Cross and Red Crescent Societies based in Panama City.

Official account on the scope of damage was so far scarce. But situations in the country described by witnesses and reporters and confirmed deaths were pointing to an appalling disaster.

At least 16 UN personnel were killed in the earthquake, UN Secretary-General Ban Ki-moon said Wednesday. As this was only a preliminary figure, more deaths were possible, he added.

The UN has said that about 150 of its employees working in Haiti are still unaccounted for, including UN mission chief Hedi Annabi and Ban's deputy special representative Luiz Carlos da Costa.

"Most urgent need is emergency search and rescue," said Ban.

Briefing the UN General Assembly, Ban said a Chinese emergency rescue team had arrived in Port-au-Prince.

Two teams from the United States were expected to arrive by Wednesday night with two more by Thursday morning, Ban said.

Additional search and rescue teams were said to be arriving from nearby Guadeloupe and the Dominican Republic with other rescue teams on their way from many other countries, he said.

"In the next few days, we will issue a flash appeal for Haiti," Ban said, adding that he expected his humanitarian coordinators to assess the necessary needs and funding.

Ban said he had ordered US$10 million  to be released from the Central Emergency Fund to kick-start relief efforts.

In response to the quake, the World Bank said Wednesday that it would provide US$100 million in emergency grant to support recovery and reconstruction in the Caribbean nation.

"This is a shocking event and it is crucial that the international community supports the Haitian people at this critical time," said World Bank President Robert B. Zoellick.

More countries and organizations pledged relief assistance on Wednesday after immediate aid announcements from the United States, the Dominican Republic, Venezuela and other Latin American countries.

China sent an emergency rescue team Wednesday evening along with 10 tons of food, equipment and medicines. China's Red Cross Society has decided to donate 1 million dollars in emergency aid.

US President Barack Obama said Wednesday that his country would take swift measures to respond to the disaster, and that he had directed the administration to focus on saving lives.

Obama said the US military had already mobilized an aerial relief team to overfly Haiti to assess the damage. Civilian search and rescue teams would begin to arrive within a few hours.