By Jessie Yeung, Laura Sharman, Lex Harvey, CNN

(CNN) — When floodwaters cascaded down deep mountain gorges and swept into a Nepali valley on Wednesday, it devastated already-vulnerable communities that sat along the swollen river, home to many ethnic groups and farmers.

But it also sent shockwaves across the world, with hundreds of foreign nationals unaccounted for. In households across the United States, India, Canada and more, people are desperately waiting for news of their missing loved ones – which include a doctor from Delaware, a New Zealand mother of two, and three young teenagers from the US and Australia.

The region is popular for tourism, trekking, and religious pilgrimage to temples and sacred sites revered across multiple faiths – all of which draw large numbers of visitors during summer and early fall. It’s also home to several foreign-backed hydropower projects.

Hundreds are also missing in neighboring China; the initial powerful landslide took place on its border with Nepal, with a mudslide then hitting China’s Gyirong Port,a major land border crossing.

Officials have not yet released names of those confirmed dead or still missing, as rescue efforts continue Thursday. But the scale of the tragedy is becoming clear, with social media filled with countless pleas for help – including from the Nepali diaspora overseas.

Here’s what we know so far about the people affected.

Ethnic groups and poor communities hit

The hardest-hit communities in Nepal sit on the banks of the Trishuli river, which winds through several districts including Rasuwa, Nuwakot and Dhading.

These districts are home to more than half a million people, according to recent census data. They represent a diverse range of ethnic groups including the Tamang, Gurung, and Newar people, some of whom have lived there for centuries.

Many rely on agriculture for their livelihoods, though some have also turned to tourism as the region has become increasingly popular for outdoor activities like trekking and rafting – as well as for religious tourism. Each summer, hundreds of Hindu, Buddhist, Jain and Bonpopilgrims travel through the area en route to Tibet’s sacred Mount Kailash.

But these communities are also highly vulnerable. Districts like Rasuwa have faced historically high poverty rates, and are on the front lines of the climate crisis, at risk of disasters like forest fires and landslides.

Many residents had spent years rebuilding their lives after Nepal’s catastrophic 2015 earthquake, which killed more than 8,000 people. Displaced from their homes, hundreds of families resettled on the low-lying banks of the Trishuli river – only to face yet another horrific disaster on Wednesday.

Nepali families and diaspora

Families across Nepal are now desperately seeking news of loved ones who were in the affected areas, who range from healthcare workers to tour operators.

Asmita Dahal, who lives in the capital Kathmandu, told CNN her family was “hoping for a miracle” for her missing younger brother, 21-year-old Suman Dahal. Suman works for a tour group bringing pilgrims to Mount Kailash, and had been preparing to return to Kathmandu from Timure, a small town on the Trishuli riverbank.

“We are worried his bus might have been swept away in the flooding, we just don’t know,” Asmita said. The last thing her brother had said to her on Wednesday was: “See you in the morning.”

The disaster is also reverberating among the Nepali diaspora worldwide, who number more than 2.1 million, and are now scrambling to contact people from thousands of miles away.

Pema D. Gurung, who owns a Nepali restaurant in New York, said he doesn’t know whether his many friends in Rasuwa have survived. “In my mind and in my heart, I’m hoping my friends are alive,” Gurung told CNN. He’s been unable to contact them because the flood cut off connectivity; his friends in Kathmandu haven’t been able to reach anybody in the area, either.

Rojina Dhungana, a resident in Ottawa, Canada, woke up on Wednesday to the news that her hometown on the Trishuli riverbank had been swept away. Thankfully, her parents were safe – but many of her former neighbors and classmates are missing.

On social media, “everybody I knew – my friends, my relatives, my community – everybody was looking, like ‘Help, help, help, this person is missing!’” she said.

Foreign nationals missing

At least 517 foreign nationals are among the missing in Nepal, according to the Nepal Tourism Board.

This includes at least 178 Indian nationals, many of whom were on pilgrimage to Mount Kailash. There are also 90 Americans, 53 Ukrainians, 51 Malaysians, 35 Australians, 33 British, 25 Canadians, and smaller numbers of people from more than two dozen other countries, according to the tourism board.

Meanwhile on the Chinese side of the border, at least 260 foreign nationals are among the 558 missing, according to state media.

Many of the missing were tourists – including teenagers. A 14-year-old American girl, and two Australian boys aged 12 and 14, were part of a tour group that’s unaccounted for, according to the tour company.

American Radhika Sharma said her parents, Ramesh and Neelam Sharma, had been among those on a religious pilgrimage. Their tour company last made contact with the group of pilgrims Wednesday morning, after they reached the border with Tibet.

Sharma hasn’t heard from them since. This has been the “worst 24 hours” of her life, she said on Thursday.

All nine South Koreans were workers sent to Nepal for a hydropower plant under construction, according to Korean officials. Nepal has pushed in recent years to tap into its massive hydropower potential, often with investments from regional partners like China and India.