Nepali residents look at floodwaters after the Balkhu River overflowed following monsoon rains at the Kalanki area of Kathmandu, July 12, 2019. Getty

New Delhi, India -- Torrential monsoon rains swept away homes and triggered landslides across South Asia, affecting millions of people and claiming at least 180 lives, officials said Tuesday. The monsoon is crucial for irrigation and groundwater supplies in the impoverished region -- home to a fifth of the world's population -- and brings relief after the unforgiving summers. But the downpours from June to September can turn deadly and have wreaked havoc again this year.

Across India, Nepal, Bangladesh and Pakistan-administered Kashmir, people, dwellings and boats in remote low-lying areas have been washed away.

Nepal

In Nepal, at least 67 people have died although flood waters have started receding. Images showed rescuers using inflatable dinghies to evacuate families trapped in flooded houses.

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Health experts have warned of possible outbreaks of waterborne diseases and called for international help.

India

Nearly 50 people have been killed in India, with two eastern states -- Assam and Bihar, which borders Nepal -- bearing the brunt of the deluge. Authorities in Assam declared a red alert Monday as the flood situation turned critical, with villages cut off by surging waters and a major highway submerged.

Photos showed residents crammed in boats carrying their belongings to safer areas in Morigaon, one of the worst-affected districts, and just the roofs of submerged homes above water. So far 11 people have died in the state and some 83,000 people displaced by flooding.

Indian fire brigade personnel and rescue workers look for survivors after a building collapsed in Mumbai, July 16, 2019. Getty

In the jam-packed industrial hub of Mumbai, the rains caused a four-storey residential building to collapse -- a regular occurrence in the country where loosely-enforced building regulations leave many edifices standing on weak foundations.

Officials rushed to dig any survivors out of the rubble. Three people were quickly removed and transported to an area hospital, but their conditions were unclear. At least two people were confirmed dead, and local politician Amin Patel told The Associated Press at the scene that there was "still a chance of about 10 to 12 families trapped under the rubble."

Patel said national military and rescue teams were on their way to join in the frantic rescue efforts.

Authorities also scrambled to reach animals marooned by the deluge at the state's World-Heritage listed Kaziranga National Park, which is home to two-thirds of the world's one-horned rhinos.

Indian one-horn rhinoceros swim through monsoon flood waters at Kaziranga National Park in India, in a July 10, 2017 file photo. Getty

In Bihar, 24 deaths were reported, with 2.5 million residents affected.

Among the dead were three children who drowned as they went to check the rising water level in a canal. Two others died while playing near a ditch filled with floodwater, the Press Trust of India reported.

Bangladesh

At least five children drowned in Bangladesh on Monday, taking the toll in the country to 34, including 18 hit by lightning and seven who drowned after their boat capsized in choppy waters in the Bay of Bengal.

Bangladeshi drivers make their way through heavy rainfall at a water-logged street during the monsoon season in Dhaka on July 12, 2019. Getty

Hundreds of thousands have been marooned by floodwater in the country's north, with one of the major Himalayan rivers, the Brahmaputra, swollen to 40 inches above the "danger level," officials said.

Pakistan

Further northwest, in the Pakistan-administered part of the Kashmir region, flash floods killed 23 people and damaged 120 houses, with the water and power supplies crippled.

The United Nations said Monday it "stands ready to work with the authorities in the affected countries as they respond to the humanitarian needs resulting from this ongoing monsoon season."