International aid agency Oxfam warned that three months into Pakistan's unprecedented flood crisis funds were drying up, putting millions at risk with swathes of farmland still under water.

The United Nations issued a record two-billion-dollar appeal for funds to cope with Pakistan's worst humanitarian disaster, which ravaged an area roughly the size of England and affected 21 million people.

The World Bank and Asian Development Bank have estimated the damages at 9.7 billion dollars -- almost twice those of Pakistan's 2005 earthquake which killed more than 73,000 people.

"Funds for the UN flood appeal are drying up and threatening the aid and reconstruction effort," Oxfam on Friday said in a statement marking the third month since heavy monsoon rains began falling in northwestern Pakistan.

"The crisis is far from over," said Oxfam’s director in Pakistan, Neva Khan.

The United Nations issued the funding appeal on September 17 in New York. Officials say around 35 percent of the appeal has been funded.

"Cases of disease are increasing and large areas remain under water in southern Sindh province," said Oxfam. "As winter approaches, seven million people are still without adequate shelter."

UN officials say 10 million people are in need of immediate food assistance and health authorities have reported 99 confirmed cases of cholera.

"The funding shortfall is so serious that existing regular food rations to 3.5 million people could be in jeopardy," Oxfam said.

Tens of thousands of families, who had sheltered in schools and other buildings, are being newly displaced as schools reopen. Officials warn that some of the worst-affected areas could take up to six months to dry out.

The United Nations joined forces in urging donors to come forward, particularly for victims in the south, part of the country's breadbasket.

Spokeswoman Stacey Winston said the United Nations and its partner agencies were doing everything possible to help the victims but warned: "It is simply not enough. We need to have more money."

"The emergency still continues in Sindh and people are surrounded by water," Winston said, adding that malnutrition, food security, health conditions and shelter are major concerns.

She said many areas in Sindh were surrounded by water, which she warned may not go down for another three months. "It is a very major concern to us."

The UN Food and Agriculture Organisation said this week it had begun distribution of wheat seed to half a million farming families affected by the floods in order to allow the current planting season to take place.

Pakistan's agriculture sector, which contributes 21 percent to gross domestic product and employs about 45 percent of the labour force, has suffered massive losses that are expected to last several years.