Video shows scale of flash flood hitting Nepal-Tibet border
Massive landslides and flash floods on the Nepal-Tibet border have caused widespread damage and left hundreds dead or missing.
Search and rescue operations are under way. Chinese state media has said there are significant casualties, while Nepalese officials anticipate "huge scale loss".
Here is what we know so far.
Buildings were submerged in Nepal's Nuwakot district
What caused the deadly landslide?
Nepal's foreign minister initially said an earthquake was reported on the Tibet-Nepal border shortly before the landslide, suggesting it may have triggered the disaster.
The United States Geological Survey (USGS) had first reported the event as a magnitude 4.4 earthquake on Wednesday, but later confirmed the incident "was instead a glacial collapse and debris flow" that "caused subsequent catastrophic impacts downstream".
Map of central Nepal showing four flood-affected districts: Gorkha, Rasuwa, Nuwakot and Dhading. A marker north of Rasuwa, across the border in Tibet, indicates the epicentre of a magnitude 4.4 earthquake. Kathmandu is shown to the south-east of the affected area. An inset map locates the region within Asia.
"Additional analysis of nearby seismic stations, long period seismic waves, and satellite imagery led to the determination that the seismic event was instead a glacial collapse and debris flow, and that no earthquake had occurred," USGS said on Thursday.
Earlier Nepali authorities had also told the BBC that a massive chunk of ice may have collapsed from a mountain, pulling down rocks and other sediments with it.
Climate change is known to be driving faster glacier melt in the Hindu Kush Himalaya region and, as rescue efforts continue, scientists are trying to piece together the exact order of events.
Simon Cook, senior lecturer in energy environment and security at the University of Dundee who specialises in glaciology, said "climate change could have an impact".
He told the BBC "permafrost is partially holding some mountainsides together, this permafrost is warming and thawing and degrading so you are going to get more landslides".
One possibility is that water from rainfall or melting ice may have destabilised the ground or ice, triggering a chain reaction.
Scientist will be looking at satellite images of exactly where the landslide occurred, whether any glacial lakes suddenly drained, and where the river might have become blocked, as well as data on recent rainfall.
Watch: BBC Nepali's Shreejana Shrestha is at a hospital in Kathmandu, where some survivors are being flown in by helicopter
A deluge of material careered towards northern Nepalese towns, including areas popular with mountaineering tourists and pilgrims. The border is around 40 miles (64.4km) north of Nepal's capital city Kathmandu.
Footage showed a wall of mud and rock sweeping away buildings, roads and vehicles, as people fled the fast-moving wave of material in the Nuwakot region.
In one video, a towering wall of water and mud was seen rushing down a gorge along the Trishuli River and enveloping the Rasuvagadhi Border check point, a multi-storey building.
Severe flooding has been reported along the Bhote Koshi, Trishuli and Narayani rivers.
Deaths have also been reported in villages on the Tibetan side of the border.
The International Centre for Integrated Mountain Development (ICIDMOD) has warned secondary flooding could occur in the coming days as a result of the debris that washed into the river systems.
In a report, the ICIDMOD said they are in the process of assessing whether the Trishuli River has been temporarily blocked in narrow sections. If it has been blocked, it is at risk of forming a landslide dam - and a second flooding event.
Authorities and scientists are continuing to evaluate the size, location and stability of any potential blockages.
Satellite images of Khadga Bhanjyang on the Trishuli River three days apart show the scale of flooding
How many people are dead and missing?
The number of people killed or missing is still becoming clear
Nepali police say at least 177 people have died. Among those killed, 64 were found in downstream areas in the Chitwan district while another 26 were found in Nawalparasi East.
In an update on Thursday morning, Nepal's National Disaster Risk Reduction and Management Authority said 826 people are still missing, including more than 529 tourists, with 466 foreigners among them.
Meanwhile, China's state broadcaster CCTV said on Thursday that the number of people missing in the mudslide disaster in Tibet's Gyirong county had risen to 558.
Among these are 260 foreign nationals, CCTV said, adding that the death toll remained at three.
It is not clear if any of the missing in the Nepali and Chinese figures have been counted twice.
The border at Gyirong is the main crossing point for tourists and traffic between China and Nepal.
Reuters Police officers carrying an elderly woman who survived the flash flood at Trishuli in Nuwakot district of Nepal
How are governments responding?
Nepal's prime minister said "the entire nation has been left shocked and deeply distressed" and that officials would coordinate with China on the response.
China's President Xi Jinping urged an "all-out" search effort, and promised stronger monitoring and early warning systems to prevent secondary impacts.
In neighbouring India, Prime Minister Narendra Modi said his government was "prepared to provide Nepal with all possible types of humanitarian assistance".
UN Secretary General António Guterres says he is "saddened by the severe flooding", adding that UN teams and partners are mobilising supplies and personnel in Nepal to support the government-led response.
The US has promised $500,000 (£367,982) in aid which will be used to cover emergency shelter, water, sanitation and other relief items for communities affected by the floods.
UK Prime Minister Andy Burnham said the British government would do "everything we can" to support British nationals in Nepal.
Aerial footage shows flash flood on Nepal-Tibet border
What countries are the missing tourists from?
Tourists from all over the world come to Nepal for its mountains and sacred sites. Official figures suggested at least 291 foreigners are among the missing, including:
- India - the Nepal Tourism board said 142 nationals from neighbouring India were missing
- Ukraine - Ukraine's Foreign Ministry said Nepal's Tourist Police informed them 53 Ukrainian nationals were missing
- Malaysia - 17 Malaysians travelling with Fishtail Tours and Travels are missing in the floods, the board said. An official at the Malaysian embassy in Nepal said more than 50 Malaysians were currently unreachable
- UK - Nepal police have confirmed that 33 British nationals are missing
- Canada - a tourism board spokesman in Nepal said that 24 Canadians have been reported missing
- US - the latest update from Nepal's tourist board is that 54 US tourists are known to be among the missing
- Australia - Prime Minister Anthony Albanese has confirmed at least 34 Australian citizens are among the missing
Smaller numbers of travellers from South Korea, South Africa, Portugal, the Netherlands and New Zealand are also among the missing.
