Millions of children are at risk of being trafficked following disastrous floods in South Asia, aid agencies have warned.

At least 450 people have been killed and more than 700,000 made homeless as a result of flash floods, which began on September 3 and have devastated parts of India and Pakistan.

Flooding has already spread to neighbouring Bangladesh and Nepal, and the situation is likely to deteriorate further as the monsoon season takes hold.

In addition to the loss of their livelihoods, vulnerable families are now facing the harrowing prospect of having their children taken away by "opportunistic" traffickers.

Human trafficking is the fastest growing criminal industry in the world, with figures indicating that there are up to 27 million people living in conditions of slavery – in forced labour or sexual exploitation – around the globe today.

Every 30 seconds, a child is trafficked, and the practice is often heightened in the wake of conflict or natural disaster.

"We know from previous disasters, such as the Bihar floods in 2008, that opportunistic traffickers will take advantage of vulnerable families in the wake of disasters, by offering to temporarily take their child to cities to find work and send back money," Tearfund's Head of Asia region, Sudarshan Sathianathan, says.

"Out of desperation, families accept the offer, without realising that their child – some as young as six years old – will be sold into the sex industry or into child labour. In some extremely sad cases, they never see their child again."

Other organisations are also concerned about children and women in particular as the long-term effects of flooding in India and Pakistan take hold.

World Vision's partners on the ground in the region have shared of children in "terribly vulnerable conditions and desperate for help".

"Urgent help and funds are needed and not enough is being done. And in conditions like this children's safety and health is affected in all ways," Sajidar Mansoor, World Vision's communications manager for Pakistan, said in a statement for Christian Today.

"In the Punjab province of Pakistan hundreds of villages have been severely affected due to the recent flash floods after heavy monsoon rains. Families don't have food, shelter, protection or any way to keep themselves clean.

"Over half the children we spoke to had diseases such as diarrhoea, malaria, skin infections (scabies) or fever. Farmers say crops have been totally destroyed. Just under half the villages have lost 100 per cent of their food stocks."

Mansoor said that his teams aren't seeing many children at risk of trafficking in the areas of recent assessment, but he added that unless urgent measures are taken, "it is inevitable the situation will get worse in terms of child health and child protection."

Yeeshu Shukla, Christian Aid's Emergency Officer for India, also had particular concern for vulnerable women in the region. He cited cases in the past where men have migrated to other states for work following a natural disaster, "leaving behind women and children".

Furthermore, Christian Aid partner Church World Service (CWS) today released a statement regarding the "dire" social and economic plight of women and children affected by the floods.

CWS spoke to a woman from Azad Kashmir, Saira, who warned that those who have been left with nothing will struggle during the coming winter months.

"With nothing to warm them, life is going to get very tough especially for women and children in these tents," she said.

Saira also said this added to the vulnerabilities women were already facing without proper shelter, and shared of her own struggle now her livelihood has been lost.

"This will make the journey back to recovery including rebuilding our home very tough," she said.