A feeble international response to Pakistan's second major flooding crisis in two years has left millions of people at serious risk of malnutrition and disease, aid groups warned Thursday.

The Pakistan Humanitarian Forum (PHF), a network of the 41 largest international charities in the country, called on the international community and Pakistan to take urgent steps with the next monsoon season months away.

"With funds drying up, millions will find it extremely hard to make it through the next few months. Donors and the government of Pakistan must step up their response immediately," said Oxfam's country director Neva Khan.

At least 2.5 million people are still without food, water, shelter, sanitation and healthcare, putting them at serious risk of malnutrition, disease and deepening poverty, said the coalition of international charities.

"The floods have exposed and deepened a food crisis in Sindh that has resulted in malnutrition rates far worse than those in sub-Saharan Africa," said David Wright, country director for Save the Children.

Around 43 percent of affected people are severely short of food and malnutrition levels were already well above the emergency threshold in the southern provinces of Sindh and Baluchistan before the floods struck.

Last September, the United Nations launched an appeal for $357 million, but it has been less than 50 percent funded, the groups said.

"Six months on, the crisis seems to have been forgotten by the international community," said Naseer Memon, chief executive of the Strengthening Participatory Organisation.

Najma Warag, a mother of three and the wife of a tailor, told reporters in Islamabad that she had found nothing when she returned to her village in southern Badin district in Sindh which was still inundated and the crops destroyed.

"If you want to see what a miserable life is, come and see us. Our children are sick, we have no home, no clothes, no money and eat only one meal in a day," Warag said.

Five foreign aid and development workers have gone missing or been kidnapped in Pakistan since August, causing international charities to become more careful.

"I think we are very concerned. There seems to be a much greater targeting of humanitarian workers in the country than was before," said David Wright, country director of Save the Children.

"There are more expat humanitarian workers being held captive in Pakistan than any single country in the world," he said.

"So even that we have experience of working in insecure areas we have to strengthen our systems... We are used to deal with situations like this in other countries. We will have to take more care, that is for sure," Wright said.

Oxfam's Khan said "security of our staff is our number one priority at all times. We don't take unnecessary risks."

Tens of thousands of people are still displaced in flood-affected areas, while others have returned home to little or nothing.

The floods have devastated agriculture and hundreds of thousands of farmers are struggling to recover. A quarter of farmers missed the planting season late last year because their land was flooded or they did not receive help in time.