More than 350mm (13.8 inches) of rain was recorded – the highest daily rainfall for August in over 140 years.
Hong Kong has been hit with record-breaking rains that have seen schools and courts shuttered, hospitals disrupted, and roads badly flooded.
More than 350mm (13.8 inches) of rain had drenched the territory by 2pm (06:00 GMT) on Tuesday, the city’s weather authorities said – the highest daily rainfall for August since 1884.
The storms follow deadly flash floods in Southern China over the weekend, which left five dead in Guangdong province and prompted a large-scale search operation involving more than 1,300 rescuers.
Videos showed water cascading down steep hillsides, breaking into whitewater streams as they rushed down the many staircases linking Hong Kong’s multitiered cityscape.
Weather authorities extended their highest “black” rainstorm warning until 5pm local time (09:00 GMT).
This was the fourth such warning issued in just eight days, breaking the record for the most frequent issuance of the city’s highest weather alert within a single year, according to China’s state news agency Xinhua.
More than 9,600 cloud-to-ground lightning strikes were recorded between 5am (21:00 GMT) and noon, Hong Kong’s weather observatory said.
The water had risen to ankle height outside Hong Kong’s largest hospital, as medical authorities announced they would be closing clinics across the city due to the downpour. Meanwhile, cars were reported submerged in water.
The weather service warned on Tuesday afternoon that a “persistent rainstorm will cause serious road flooding and traffic congestion”.
The city’s Chief Secretary for Administration Eric Chan urged the public to stay alert and said employers should consider flexible working arrangements that prioritise employee safety.
Airports across the region reported cancellation rates of around 20 percent on Tuesday, according to data from Flightmaster, while speed limits were lowered due to poor visibility.
Extreme rainfall and catastrophic flooding, which meteorologists link to climate change, pose mounting challenges for both Hong Kong and mainland China. In addition to the deaths and injuries, such floods can displace thousands and threaten billions of dollars in economic losses.
Hong Kong typically receives an annual average of 2,200mm (86.6 inches) of rainfall, more than half of which usually falls from June through August.