The first patients turning up at hospitals and makeshift clinics in Indonesia's Aceh province — the area hit hardest by the earthquake and tsunami — had mostly scrapes, bruises and broken bones. Now, some doctors say they are treating worse problems, like gangrene (search) and pneumonia (search).

Dr. Ronald Waldman, who is coordinating the World Health Organization's (search) efforts in Indonesia, said dangerous infections are sneaking into superficial wounds. Measles has become a major threat, and UNICEF (search) said it expects to start mass vaccinations in the area soon.

WHO warned that if basic needs — particularly access to safe drinking water — are not restored by the end of this week, there would be a risk of infectious disease outbreaks that could kill as many people as the tsunami's direct impact.

"Five million people have been severely affected by the tsunamis. We now estimate that as many as 150,000 people are at extreme risk, if a major disease outbreak in the affected areas occurs," said WHO Director-General Dr. Lee Jong-wook, who was touring a stricken part of Aceh on Indonesia's Sumatra island Wednesday with UNICEF chief Carol Bellamy.

Scratches suffered in the disaster have now become infected and more patients are being treated for these than anything else. In some cases gangrene has set in, requiring limb amputations. There were no exact numbers on gangrene cases.

Pneumonia has also emerged as a significant illness, caused by exposure to dirty water during the tsunami, Waldman said.

However, the number of cases of children with severe diarrhea is still low, and the cases are not thought to be due to the germs that cause cholera or other illnesses that could explode into epidemics, Waldman said.

In another positive sign, the size of refugee camps that have formed so far for tsunami survivors in Asia's hardest-hit areas is smaller than usual for major humanitarian disasters, reducing the risk of disease outbreaks that could multiply the death toll, Lee said.

Lee said he was encouraged that mega-camps, such as those in Sudan's troubled Darfur region, have not formed here.

At least three Darfur refugee camps house more than 150,000 people each. A killer outbreak of hepatitis E, found in dirty water, took hold last year. International agencies estimate that disease, malnutrition and clashes in the Darfur camps have killed more than 70,000 people since March.

"A huge camp means everything will be huge — the challenge will be huge," Lee said as he visited hospitals and clinics tending thousands of people injured in the Dec. 26 earthquake and tsunami.

Mega-camps are often plagued by food shortages, poor sanitation and social unrest caused by cramped, unnatural living conditions. Infectious diseases such as cholera, typhoid and dysentery spread easily.

About 150 small, informal refugee camps have sprung up in Aceh in the week since the tsunami hit.

Such small camps are better for refugees' mental health, and let survivors live a more community-like life, Lee said.

But disease outbreaks are still a threat, he warned.

"Living in even those little camps is not a good idea," added UNICEF's Bellamy. "The sanitation system is still quite unacceptable."

Meanwhile, Michael Elmquist, head of the U.N. relief effort in Indonesia's Aceh province on Sumatra, said on Wednesday that Indonesia's government has broken ground on four refugee camps that could house up to 500,000 people. He did not provide details on the size of the planned camps.

Three of the five hospitals in the provincial capital, Banda Aceh, are functioning, staffed by Indonesians and foreign helpers, but they are struggling to find enough beds. The U.S. military has been evacuating injured survivors from remote communities.

Bellamy said sanitation is the most desperate challenge in Banda Aceh.

Bottled drinking water is getting through, but toilets are almost nonexistent.

The two UN officials said they were encouraged to see people clearing wreckage left by the tsunami.

"The damage is mind-boggling, but they are rebuilding and everybody is moving around with a purpose," Lee said.

Bellamy said she was impressed with the scale of the cleanup.

"There are more signs of cleanup here than there were in the four locations in Sri Lanka I was in two days ago," she said.