At least 14 people have died in Taiwan's eastern county of Hualien, with 124 missing after a barrier lake in the mountains overflowed to deluge a town during a typhoon, the island's fire department said.
Taiwan has been lashed since Monday by the outer rim of Super Typhoon Ragasa, now heading for China's southern coast and Hong Kong.
The barrier lake, formed by landslides triggered by earlier heavy rain in Taiwan's sparsely populated east, burst its banks on Tuesday afternoon to send a wall of water into the township of Guangfu.
Fire officials said all the dead and missing were in Guangfu.
36,000 Olympic-sized swimming pools
Wang Tse-an said his entire village of Dama, home to about 1,000 people, had been flooded and many were still stranded.
"It's chaotic now," Wang, the village chief, told the Reuters news agency, saying the most important task was to get people to safety in shelters, while supplies could not get through.
"There are mud and rocks everywhere. Some flooding has subsided, but some remains," he said.
The government estimated the barrier lake contained 91 million tonnes of water, enough to fill about 36,000 Olympic-sized swimming pools and the equivalent of a major reservoir in southern Taiwan.
The lake overflowed, releasing approximately 60 million tonnes of water, the government said.
The typhoon brought approximately 700mm of rain to Taiwan's east.
Flights axed, schools shut as typhoon nears Hong Kong
Meanwhile, parts of southern China and Hong Kong were on high alert as the super typhoon approached, bringing powerful winds and lashing rain, which forced Chinese authorities to shut down schools and businesses in at least 10 cities.
The Hong Kong Observatory issued its highest typhoon warning, saying it will "remain in force for some time".
It also warned of significant swells and storm surge as the storm moves through, with some areas potentially seeing water levels four to five metres above normal.
There were no flights out of Hong Kong after 8pm AEST on Tuesday, according to the airport's website. Qantas and Cathay Pacific had earlier signalled that the majority of their flights were set to be cancelled.
Hong Kong's number-two official, Eric Chan, had earlier said Ragasa would pose a "serious threat" comparable to the super typhoons of 2017 and 2018, which caused hundreds of millions of dollars in property damage.
Ragasa is expected to make landfall in the central and western coastal areas of Guangdong within 12 hours, the province's emergency management bureau said on Tuesday.
Scientists warn that storms are becoming more powerful as the world warms due to the effects of human-driven climate change.
