Two US Marine cargo planes carrying a mobile field hospital landed Tuesday in Yogyakarta, closest to the quake area in central Java, after cracks in the airport runway were patched.

A disaster assistance response team from the US Agency for International Development is being readied and the amphibious assault ship USS Essex, which has extensive medical facilities, is en route to the area, White House deputy press secretary Dana Perino said.

The United States also increased its aid contribution to $5 million.

The United Nations said at least 21 other countries have joined the effort to help those left homeless by Saturday's magnitude-6.3 quake, which killed more than 5,800 people. An estimated 647,000 people were displaced by the quake, nearly a third of them homeless and the rest staying with relatives, said Bambang Priyohadi, a senior provincial government official.

The government said Wednesday the temblor destroyed more than 135,000 homes, reducing them to piles of bricks, tiles and wood in less than a minute. Priyohadi based the displaced figure on the number of homes destroyed and a family index of 4.8 people per house.

The main hospital in hardest-hit Bantul district was still overwhelmed, with 400 patients for just over 100 beds, and doctors complained of a lack of supplies.

"We are short of splints, gauze, even beds," said Dr. Hidayat, the hospital's earthquake emergency coordinator, adding that 90 percent of the victims had bone fractures. "The minute we get fresh splits, they are gone."

But conditions improved at several other hospitals, where parking lots and hallways that had been filled with hundreds of victims in the days after the quake were clear, with most patients now being treated in beds.

Workers removed a tent outside Yogyakarta's largest hospital, Sardjito, that had been used to shelter the injured.

The UN's top humanitarian official said the aid effort was going well, and there had been major improvements in coordination among aid organisations and nations since the 2004 Indian Ocean tsunami that killed 131,000 people in Indonesia's Aceh province alone.