More than half a million (548,816) families have lost their homes, said the UN agency.

Flooding has come at a time when Bangladesh is still recovering from Cyclone Amphan, and its already stretched emergency and health response systems are working hard to contain the spread of the COVID-19.

The country now has over 210,000 confirmed cases.

UNICEF said it is working closely with government partners, who are leading the flood response, and NGOs to provide urgently needed water, sanitation and hygiene supplies to children and communities in need.

UNICEF is also "actively engaged" in supporting a comprehensive outbreak response across the country.

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Weeks of torrential monsoon rains, widespread flooding and deadly landslides in Bangladesh, India and Nepal have affected millions of children and families, the agecy said.

Over four million children are currently estimated to be affected and in urgent need of life-saving support, with many millions more at risk.

"Even for a region that is all-too-familiar with the devastating impact of extreme weather, the recent heavy monsoon rains, rising floods and continued landslides are creating a perfect storm for children and families affected,” said Jean Gough, UNICEF Regional Director for South Asia.

"The COVID-19 pandemic and containment and prevention measures add an additional complication to the mix, as COVID-19 cases are accelerating in some of the affected areas,” she added.

Over 700 people have died and dozens are missing across the four countries, with continuing reports of children drowning.

UNICEF said it is on the ground working in close coordination with respective governments and humanitarian partners to scale up its responses and support the immediate needs of affected children and their families, but the response is complicated by the COVID-19 pandemic and the associated containment and prevention efforts.

Measures such as physical distancing and handwashing need to be observed in order to minimize the risk of infections among affected populations, especially those in emergency shelters.

Many areas remain inaccessible due to damage to roads, bridges, railways and airports.

The most urgent needs for children are clean water, hygiene supplies to prevent the spread of disease, food supplies and safe places in evacuation centres for children to play.

"The fall-out from the COVID-19 pandemic is being compounded by climate change and extreme weather events and are arguably the biggest issues affecting children in South Asia right now," said Jean Gough.

"Immediate support, more resources and innovative programmes are urgently needed to address the challenges that these threats represent to the region’s children.”

In India, over 6 million people across Bihar, Assam, Odisha, Gujarat, Maharashtra, Madhya Pradesh, Kerala, Uttarakhand, Uttar Pradesh and West Bengal have been affected by the floods, including an estimated 2.4 million children.

Though flooding at this period of the year is common, this widespread scale of floods during mid-July is unusual.

At the same time, India has seen the daily number of COVID-19 cases crossing the 30,000 thresholds. UNICEF is working with the government and partners to respond quickly and effectively.

UNICEF is also supporting the Government of Assam to implement the COVID-19 adapted relief camp management guidelines and Child Friendly Spaces in select districts, in addition to its focused support for maternal and child health service continuity and COVID-19 response in many states.

In Nepal, heavy monsoon rainfall has caused flooding and landslides across different parts of the country, impacting more than 20 districts, since 9 July.

More than 100 people have died, 48 are missing and feared dead while 87 are injured. Over 10,000 people - half of them children - have been affected with an estimated 7,500 displaced from their homes.

This same period has also seen a significant number of COVID-19 positive cases in Nepal.

UNICEF has so far been responding to the immediate needs in the central and far western areas of Nepal where landslides have occurred, providing blankets, tarpaulin, hygiene kits, buckets, mugs and water purification tabs. UNICEF remains at the forefront to support the delivery of essential as well as COVID-19 related health services.

UNICEF is also planning to provide further support for landslide and flood victims.

In Bhutan, the monsoon rain has caused landslides across the country and is hampering transport and communication as the main highway and inter-district roads have been damaged.

The flashfloods were caused by the overflow of the seven streams and tributaries to the Mao river.

The water levels in the Mao remains very high posing significant risks for more flooding.

The flooding has also caused damage to crops and a water treatment plant.

So far four people have died because of the flooding, said UNICEF