It's been nearly a week since Nepal's catastrophic floods, and the area where most missing Australians were last heard from remains so cut off that not even a vehicle can get in. Gyirong Port, the border crossing between Nepal and China, was the first to be hit. Chinese rescue teams who managed to reach it by helicopter or on foot describe a scene of total flattening - immigration building, power lines, everything, just wiped away.

News that phone connectivity was restored spread quickly on Monday among families of lost Australians gathered in Kathmandu, who shared updates via WhatsApp and Facebook. One family member, who wished to remain anonymous, told the Guardian she had been trying to ring her husband all morning after hearing the line was back. He didn't answer. “The embassies aren’t helping,” she said.

The number of missing Australians rose to 43 on Monday, with at least 33 believed to have been near Gyirong Port just before impact. Among them: 15 from Himalaya Glacier Company, 11 from Isha Foundation, six from Kailash Journeys, and one from Kathmandu Holiday Tours and Travel - many arrived at the immigration building just 10 minutes before the flood hit.

Sujan Wasti, head of Kailash Journeys' Nepal operations, last heard from his group at 7:30 am when the guide said they were coming back. They were scheduled to land in Kathmandu on Thursday. “In the area, the rescue has been done,” he said. “Now, it will just be about collecting the bodies and bringing them [home].” Since last Wednesday, Wasti has sent teams up the Trishuli River, flown over the border twice by helicopter, and visited local hospitals - all to no avail. “We are searching every place we can, but still we have not found anyone,” he said. “Along the border, it was only dead bodies. If they are alive, it will be a miracle.”

China is coordinating the search and rescue. As of Monday morning, crews had 1.15km of road left to clear and reconstruct to reopen the highway on the Tibet side. Since Friday, only rescue crews have accessed the area - some hiking 10 hours, then rappelling into the valley; others, when weather allowed, helicoptered in.

Akhilesh Surjan, a disaster management expert at Charles Darwin University, said one “sensitive question” is how long to keep hope alive. “The rescue experts consider the first 72 hours to be very critical,” he said. “After the first 72 hours, the chance of finding survivors drops sharply.” Still, he noted survival after three days “is not uncommon” - after Japan's 2011 earthquake, two people were found alive after nine days. Survival depends on factors like air pockets, protection from weather, and lack of severe injuries. He said possibilities include being swept downstream and stranded, or sheltering in a place not completely destroyed.

Getting into Gyirong Port isn't the only challenge. Thick mud and pools of water have made life-detection devices unreliable, so rescuers are calling out as they search. Rain is forecast for the next two days, complicating efforts, and there's the threat of another flood or landslide - a hazard analysis on Monday found “high-risk geological disaster points.” Surjan noted that rescue teams would be analysing the landscape to predict where people might have moved, but it's dangerous work. At least 85 rescuers, including police and army officers, are now missing in Nepal.

Three days after the disaster, the first Chinese rescue team reached the border complex and found everything destroyed. Rescue worker Zou Mingqi told Chinese state media, “There was no road … it was all virgin forest and sheer cliffs.” At the complex, “as far as the eye could see, there was nothing but ruins.”

The Isha Foundation has sent volunteers to Kathmandu and Tibet to help families. Their loved ones were inside the immigration centre, about to cross the border, when disaster hit. On Sunday, the foundation told families to “expect the worst.” The valley is covered with debris, possibly 13-15 metres of silt; the flood waters may have risen as high as 45 metres with immense force, completely wiping out the building complex. “We wish with all our hearts that we could offer you something more hopeful,” the foundation wrote. “Everything our teams have seen, and everything those closest to the site have shared with us, has led us to expect the worst.”