Wednesday's catastrophic flood caused by a glacier collapse killed 547 people in Nepal and five in China's Tibet, with almost 1000 more missing in the two countries.
A huge torrent of rock, ice, mud and debris cascaded through Himalayan mountain river systems after the collapse, and also led to the formation of a lake where water continued to collect and rise.
On Friday, the lake's reservoir had topped 2.5 million cubic metres of water, up from the estimated 1.5 million-2 million cubic metres recorded a day earlier, before overflowing into the Lhende Khola river and then into the Trishuli, authorities and witnesses in Nepal said.
The overflow sparked panic and warnings from authorities in Nepal, leading to rescue operations being suspended for about three hours.
The risk of the lake bursting had prompted all Chinese rescue personnel and vehicles to withdraw on the Chinese side as well and stand by in a safe area, state broadcaster CCTV said.
Both resumed rescue operations after the threat eased.
"By noon, as the risk posed by the upstream dammed lake was deemed manageable, rescue operations for the Gyirong mudslide disaster quickly resumed and were stepped up," Chinese state broadcaster CCTV said.
Nepal's army spokesperson Raja Ram Basnet told Reuters that rescue operations had been temporarily halted after the flood alert but it was found that the rise in the water level was only by about half a metre.
Wednesday's flood ripped through villages and valleys, destroying power stations, roads and bridges along a route that links Kathmandu with Lhasa in Tibet and is popular with trekkers and pilgrims.
Of those missing, at least 540 are foreigners, of which 38 are Australians - many of them Hindu pilgrims from India headed to the holy Mount Kailash and Lake Mansarovar in Tibet.
More than 90,000 people are estimated to be affected, the Red Cross said, adding that trucks with relief supplies were blocked after the barrier lake broke its banks.
In Beijing, China's Politburo met on Friday to direct rescue work, state media reported.
Authorities must "scientifically formulate search-and-rescue plans, make every effort to search for missing people from China and abroad", the meeting chaired by President Xi Jinping said, according to state news agency Xinhua.
The meeting called for stronger monitoring of glacier lakes, landslide risks and barrier lakes, emergency aid to affected areas in Nepal, and closer international disaster co-operation.
Chinese rescuers had yet to reach the worst-hit site on the Chinese side of the border, the Gyirong border crossing, by Thursday evening, state media reports indicated, as crews worked to clear debris from the key access road leading to the area.
Dramatic footage on Wednesday showed enormous torrents of muddy water and debris tearing through structures in the border crossing area within seconds and engulfing people trying to flee.
The tally of missing in Tibet's Gyirong County was 558, Chinese state broadcaster CCTV said on Thursday, including 260 foreign nationals.
So far, just five people have been confirmed dead on the Chinese side.
Earlier, Nepalese rescue teams used helicopters to search for survivors and drop emergency supplies to thousands cut off in towns and valleys, while emergency services - some using sniffer dogs - recovered dozens of bodies swept down into the plains.
While offers of assistance are pouring in, Nepal said it does not need help from other nations in search and rescue missions.
A South Korean rapid response team is already in Kathmandu but has not been deployed because the Nepali government does not have a plan to accept foreign rescue yet, according to the foreign ministry in Seoul.
The Kathmandu Post reported that India, China, the United States, Britain, Japan, South Korea, Sri Lanka and Bangladesh had asked the government to allow their search-and-rescue teams to assist in the operation.
