The spread of disease has become a major concern in Haiti, medical experts said today, as relief groups struggled to speed up the delivery of supplies to hungry and thirsty earthquake survivors.

While a slight return to normality street vendors emerging to offer fruit and vegetables, rescue teams from around the world continued to search for survivors under the rubble of collapsed buildings. More successful rescues were being reported six days after the disaster but tens of thousands are still believed to be buried.

A baby boy injured in last Tuesday's earthquake rests in the university de la paix hospital in Port-au-Prince January 18, 2010. (REUTERS/Daniel Aguilar) Medical experts said many survivors had multiple fractures and internal injuries. Medical teams at mobile hospitals that have been overwhelmed by the casualties warned of the immediate threats of tetanus and gangrene and the spread of measles, meningitis and other infections.

In Haiti, where Aids, tuberculosis and malaria are rampant, children are malnourished and hygiene is already a challenge, the quake has added potentially lethal infections, broken bones, internal injuries and other health complications.

"By any stretch of the imagination it is going to be incredibly difficult. The population in Haiti was already vulnerable and faced enormous health threats," one expert said.

US troops were continuing to protect the distribution of aid as it began arriving more regularly at Port-au-Prince airport, and a US air force cargo plane began dropping supplies into a secured area five miles north-east of the shattered capital.

Bill Clinton, the former US president and UN special envoy to Haiti, pitched into the aid effort by unloading bottles of water from a plane and touring a hospital where supplies were tight.

"It's astonishing what the Haitians have been able to accomplish, performing surgeries at night ... with no anesthesia, using vodka to sterilise equipment," he said.

The US military hopes to reopen Port-au-Prince port in two or three days, but are relying for now on helicopters to distribute food and water.

A C17 cargo plane, flying a round-trip from a North Carolina base, dropped 14,000 packaged meals and 14,000 litres of water, while the US army's 82nd Airborne set up a base at the Petionville club to distribute water and meal packs to the 50,000 survivors who set up tents on Haiti's only golf course. Exhausted soldiers slept on the tennis courts.

Despite reports of lawlessness, US military officials said violence was isolated and not impeding the aid mission.

As the US military and relief groups struggle to speed up delivery of aid, thousands were leaving the capital, having lost patience with the massive but ponderous aid effort. Most of those fleeing said they were heading to small farms run by relatives.

"We've got no more food and no more house, so leaving is the only thing to do," Livena Livel, a 22-year-old street vendor, told Associated Press. She was going to her father's house near the town of Les Cayes, four hours south of Port-au-Prince.

"At least over there we can farm for food," she said, carrying her one-year-old daughter, Othmeline.

Livel and the six relatives leaving with her said they'd scraped together the last of their money to pay for the trip. With petrol scarce, bus drivers have ramped up fares, forcing some to pay more than three days' wages for a seat.

No one has begun to estimate the number of injuries from the magnitude 7 earthquake that destroyed much of the capital a week ago. Haitian officials said the death toll was likely to be between 100,000 and 200,000.