What we know about deadly Nepal-Tibet floods
Devastating landslides and flash floods on the Nepal-Tibet border have caused widespread damage and left hundreds dead and thousands more missing.
More than 700 people have been killed and at least 2,400 people remain unaccounted for, according to Nepal's National Disaster Risk Reduction and Management Authority.
At least 16 people have died in Tibet, with another 546 reported missing by Chinese state media.
On Wednesday, flood water tore through the border region, sweeping away homes and roads, local officials have said.
Rescue workers say they now face a critical moment to reach remaining survivors as fears mount of further flooding in the disaster's aftermath.
Here is what we know so far.
What caused the landslide?
Initial reports of an earthquake on the Nepal-Tibet border led many to believe that a tremor had caused a landslide, which in turn caused the devastating floods early on Wednesday.
However, the US Geological Survey (USGS) later confirmed that the disaster was caused by a "glacial collapse" - when a glacier or part of a glacier disintegrates.
The impact of the collapsed glacier hitting the bottom of a valley was so powerful that it registered a magnitude of 5.2, according to the agency, causing "subsequent catastrophic impacts downstream".
Powerful flood water and debris travelled some 62 miles (100km) downstream from the Trishuli and Bhote Koshi Rivers, the USGS said, sweeping through towns popular with mountaineering tourists and pilgrims in northern Nepal.
Footage showed a wall of mud and rock sweeping away buildings, roads and vehicles as people fled 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 Rasuwagadhi Border checkpoint, a multi-storey building on the Nepalese side.
Gyirong Port, over the border, was also hit. A number of deaths were reported in Tibetan villages.
Scientists are trying to piece together the exact order of events as rescue efforts continue. Mike Searle, professor of Earth sciences at Oxford University, said the glacier could have collapsed "hours or days" before the flooding hit Nepal and Tibet.
"I think the sheer wave of debris suggests there was a landslide first, the water built up, [which] dammed the river, and then it burst in one huge great flood," he told the BBC.
The International Centre for Integrated Mountain Development (ICIDMOD) has warned secondary flooding could occur in the coming days as a result of debris that washed into the river systems.
The ICIDMOD said it was assessing whether the Trishuli River had been temporarily blocked in narrow sections. If this is the case, it is at risk of forming a landslide dam and a second flood.
Separately, China has warned there was a "high risk" a lake that formed after the landslide may burst its banks, causing fresh flooding downstream. As of Friday, an estimated 2.5 million cubic metres of water had accumulated, according to broadcaster CCTV.
State media reported that rescue operations were briefly suspended on Friday after the lake, which has formed at the confluence of the Chhochen Khola and Purepu Tsangpo rivers, overflowed - before water levels dropped slightly. Heavy rain is forecast over the next few days.
But experts have told the BBC that it was possible that the lake could drain naturally over time.
How many people are dead and missing?
The number of people killed or missing is still becoming clear.
At least 734 people had died as of Sunday and 2,498 are still missing, according to the country's disaster agency.
The government has released a list of more than 261 foreign nationals who have been out of contact since the floods hit.
Meanwhile, 16 people have died in Tibet and 546 are missing, China's state broadcaster CCTV has reported. These figures have not been independently verified and it is unclear whether any of the missing in the Nepali and Chinese figures have been counted twice.
Tibet, which China annexed in the 1950s, is one of the most strictly controlled regions in the country. It is virtually impossible for foreign media to gain entry there and trying to contact local residents is just as hard.
Brigadier General Rajaram Basnet, a spokesman for Nepal's army, told the BBC that rain and unpredictable weather in the area were making rescue operations increasingly challenging.
Which countries are the missing tourists from?
Tourists from all over the world come to Nepal for its mountains and sacred sites. Reports of those missing include the following:
- India - at least 320 Indian nationals are missing, the foreign ministry in Delhi says
- China - The Chinese foreign ministry says nearly 100 Chinese nationals are missing in Nepal
- US - 90 Americans are still missing, the US state department says
- Ukraine - 62 Ukrainian nationals are missing, Nepalese police say
- Malaysia - 51 Malaysians travelling with Fishtail Tours and Travels are missing in the floods, officials say
- Australia - 41 Australians are unaccounted for, according to the country's assistant immigration minister
- UK - Nepal's police say 33 British nationals are missing; Chinese state broadcaster CCTV also reports 15 British nationals are among the missing in Tibet - it is unclear how many of those are included in the figure reported by Nepal
- Canada - 30 Canadians are missing, says the country's foreign ministry
Smaller numbers of travellers from countries including South Korea, South Africa, Portugal, the Netherlands and New Zealand have also been reported missing.
How are governments responding?
ReutersNepal's priority is to locate the missing and provide urgent relief, Foreign Minister Shisir Khanal said on Saturday, with more than 4,450 people rescued so far.
He said authorities were co-ordinating with families to identify those missing, and diplomats were facilitating communications with the relatives of missing foreign nationals.
He said the risk of possible secondary flooding was being monitored, with officials on "high alert".
Additional personnel were deployed on Friday in the hopes of speeding up recovery efforts, the office of Prime Minister Balendra Shah said.
Chinese President Xi Jinping chaired an emergency meeting of officials to co-ordinate rescue efforts the same day, according to Chinese state news agency Xinhua.
Kamal Kishore, special representative of the UN secretary general for disaster risk reduction, urged countries to support response efforts.
The US previously promised $500,000 (£367,982) in aid for communities affected by the floods, while the UK said it had offered £5m.
Meanwhile, the Indian Air Force said that military cargo planes carrying nearly 50 tonnes of supplies had been sent to Nepal.
Might climate change have played a role?
Climate change is known to be driving faster glacier melt in the Hindu Kush Himalaya region.
Geologist Daniel Shugar – one of the first experts to suggest Wednesday's flash flooding could have been caused by glacial activity – said glacial thinning caused by global warming could increase the risk of landslides.
But it is still too early to definitively link the event to climate change, Shugar, who is based at the University of Calgary in Canada, told the BBC.
Simon Cook, a geoscientist at the University of Dundee, said that climate change "could have an impact".
He said his team believed they had identified where the collapse had occurred. He told the BBC that the lower part of a glacier in Nepal near the Langtang Lirung peak - approximately 15km west of the site of the floods - had collapsed.
Cook estimated that the glacier collapsed in a north-westerly direction and then travelled westwards downstream.
He told the BBC that "permafrost is partially holding some mountainsides together, this permafrost is warming and thawing and degrading so you are going to get more landslides".