As rescue efforts started in the disaster-hit Port-au-Prince on Thursday, casualties of Haiti's devastating earthquake remained difficult to anticipate.

In the streets of the massively-damaged capital, fearing possible aftershocks, some survivors set up camps while others prepared to stay up through the dark night.

Tons of medicines, food and shelters as well as teams of rescuers from China, France and Spain are beginning to land at the still functional airport in the city of Port-au-Prince.

The Chinese international search and rescue team, which comprises 50 members, has arrived at the airport of the heavily damaged capital of the Caribbean country, where it was immediately split into two units.

Of the two units, one was sent to the hardest-hit downtown area of the city for search and rescue while the other unit was missioned to set up communication and logistic equipment at the place where Chinese peacekeepers in Haiti are stationed.

The Chinese rescuers are now working against the extreme difficult circumstances of crumbled walls and twisted steel bars at the used-to-be U.N. headquater in Haiti, seeking traces of any possible survivors.

Three French planes are to evacuate around 60 injured people to hospitals in the Caribbean islands of Martinique and Guadeloupe, said French Foreign Minister Bernard Kouchner.

Meanwhile, many more countries have reached out their helping hands, either in direct donations or sending additional assistance goods.

The Japanese government has decided on Thursday to donate 5 million U.S. dollars to Haiti for emergency disaster relief, plus some other aid such as tenets worth about 330,000 dollars. It also sent a search and rescue team, announced Japan's Chief Cabinet Secretary Hirofumi Hirano.

Britain on Thursday announced an aid package of 6.15 million pounds (10 million dollars) to the quake-ravaged country in the Caribbean.

Additionally, a team of 75 rescuers and emergency assessment personnel were due in Port-au-Prince during the day to help with the rescue efforts.

India was also ready to give 1 million dollars to help Haiti coping with the disaster, an Indian External Affairs Ministry statement said on Thursday.

The United States will send 300 medical professionals to Haiti and 3,500 troops on Thursday to Haiti for disaster relief and security, U.S. Army sources said.

The International Monetary Fund will provide 100 million dollars of aid to Haiti, IMF chief Dominique Strauss-Kahn said Thursday.

While constant flow of assistance is pouring into the Haitian capital, it is still unclear and difficult to estimate the causalities of the magnitude-7.3 earthquake.

"Let's say that it's too early to give a number," said the Haitian President Rene Preval.

U.S. Secretary of State Hillary Clinton also said it's still too early to make a firm estimate of the number of deaths in the wake of Tuesday's devastating earthquake.

"Haiti has been devastated by this earthquake," said the chief U.S. diplomat, "It is beyond our comprehension."

A senior Haitian Red Cross official said the death toll could be between 45,000 and 50,000, with a further 3 million affected.

Brazilian military sources said on Thursday that 14 Brazilian peacekeepers lost their lives in the earthquake, revising the previous number of 11. Another 12 badly-wounded soldiers will be brought back to Brazil for medical treatment, the sources added.

More than 100 U.N. staff members are believed to remain missing after the strong quake on Tuesday, a United Nations spokeswoman said Thursday.

"Over 100 people are unaccounted for," said Elisabeth Byrs, spokeswoman of the U.N.'s Office for the Coordination of Humanitarian Affairs.