At least eight hospitals in the Haitian capital of Port-au-Prince have been severely damaged or destroyed while those few that remain open have been overwhelmed by patients or people desperately searching for loved ones.
Medecins Sans Frontieres has set up a number of makeshift-tent clinics in the city where they had treated upwards of 2,000 people by last night.
The organisation's 800 staff on the island were yesterday joined by the first contingents of anaesthetists, trauma surgeons and other specialists, with more staff and inflatable operating theatres on the way.
A US navy hospital ship with 12 operating rooms is due to arrive within days.
Aid agencies fear the large number of bodies left unburied in the streets could trigger disease and epidemic.
Magalie Boyer of the aid group World Vision said the largest hospital in the city, l'Hopital General, was functioning but was overwhelmed by fatalities and casualties.
The partially collapsed Canape Vert hospital was also working. Many Haitians were crossing the Dominican Republic border into the city of Jimani, where a small hospital is caring for many serious injuries, she added.
The World Health Organisation is recommending treating the bodies with chemicals and placing them in shallow pits to allow their loved ones to identify them, rather than resorting to mass graves.
Jean-Claude Fignole, Action Aid's Haiti director, said: "Haiti needs a massive clean-up. There are bodies everywhere, and hundreds of thousands of survivors are living in very close proximity to the dead. The potential for disease is staggering."