Aid groups warned on Wednesday that vital relief efforts for five million people affected by floods in Pakistan's fertile southern belt could be cut back because of a shortfall in foreign donations.

Supplies of clean water, sanitation, food, shelter and healthcare are all under severe threat and impoverished farmers in waterlogged Sindh face losing yet another winter crop, just as the cold weather closes in.

The badly affected province was already reeling from floods last year that were the worst ever in Pakistan.

Less than a third of the UN's $357 million floods appeal for 2011 has been met and global aid organisations Oxfam, Save the Children, Care and umbrella group ACTED are urging donors to give more or see aid flows stop.

"Over two months into the crisis, millions of people are still without basics. If relief operations stop, it could lead to an unimaginable catastrophe," said Neva Khan, Oxfam's country director in Pakistan.

"With winter approaching fast, millions of people who are still without shelter will be left out in the cold. We urgently need to see the same donor generosity and giving that took place last year during the floods."

Save the Children has raised only 35 percent of its required funds, while Care faces a shortfall of 91 percent.

The United States and European Commission have given the most money to the United Nations appeal, donating $13.4 million and $20.6 million respectively.

Stacey Winston, from the UN, said the 2011 fund "remains distressingly underfunded with a 73 percent shortfall and if more funding is not received relief supplies will run out within weeks."

According to official figures, more than 1.58 million homes in Sindh and 26,000 in neighbouring Baluchistan province have been damaged in the flood disaster. About 800,000 people remain displaced.

Latest estimates suggest that three million people are in urgent need of emergency food supplies.

Farmers badly need help to plant a new season of crops or find other ways to earn a living, while millions of others are at risk of disease from stagnant waters, raising the risk of malaria, dengue and respiratory disease.

"We had expected the situation to stabilise by now but conditions are going from bad to worse," warned Save the Childrens Pakistan country director David Wright.

"Malnutrition levels among children under five are among some of our worst-recorded cases."