"They are exhausted. They are working long hours and they really need support," Kunii, chief of health and nutrition for UNICEF in Myanmar, told Reuters in a telephone interview.

Many survivors had laceration wounds on their backs and legs from the surge of water and debris whipped up by winds of 190 kph (120 mph), he said, citing reports from UNICEF field teams.

They also saw many cases of dehydration and diarrhoea, with the latter afflicting up to 20 percent of children in some areas hit by the cyclone which killed nearly 23,000 people and left another 1.5 million destitute.

UNICEF was sending essential medicine kits to hospitals desperately short of supplies in the five declared disaster areas, home to 24 million people.

"They need sutures, bandages. They need blood, antibiotics, rehydration solutions for diarrhoea," Kunii said. "They are full of patients and they cannot be treated properly due to a lack of human resources and drugs."

The military government has sent doctors into the delta eight days after the disaster, but Kunii said a larger international response was needed. The regime has been criticised for its slow approval of visas for foreign aid experts.

The former Burma has a relatively large number of overseas-qualified doctors, but the government health system is in tatters after 46 years of military rule.

The regime spends only a few dollars per person on its 53 million people, who already faced some of the highest rates of disease in Asia before the cyclone struck.

Kunii, a veteran of the 2004 Asian tsunami which killed at least 230,000 people, said there were local outbreaks of disease at the time. But fears of epidemics causing tens of thousands of deaths did not come true because the aid response was swift.

Emergency supplies are trickling into Myanmar, but it pales in comparison to the massive airlifts after the tsunami when foreign medical teams had access to disaster areas.

In post-cyclone Myanmar, the lack of clean water was one of the biggest threats to health, Kunii said.

"We have observed people drinking very dirty water from ponds, he said.

UNICEF was setting up a surveillance system for water-borne diseases such as cholera, which is mainly transmitted through contaminated water and food.

A common fear that cholera epidemics are also caused by dead bodies after disasters is false, according to the World Health Organisation.

Malaria was also endemic in the delta region which could see outbreaks in 3-4 weeks, Kunii said.

"We should be ready and prepared for a worst-case scenario. It means outbreaks of cholera, malaria, dengue fever," he said.