The hail and rain on Sunday was a wake-up call for Hongkongers about the fast-changing climate that could disrupt lives and businesses within moments, a veteran meteorologist says.
Watch: Giant hailstones batter Hong Kong
The warning by Leung Wing-mo came as the drainage department chief said the city's drains could be close to their limit for handling downpours, and as rainstorms continued to batter Hong Kong and the region.
Leung, a spokesman for the Hong Kong Meteorological Society, said extreme weather could become routine if global warming accelerated.
"The bad weather might have yet to expose our systemic weaknesses, but it is definitely a wake- up call for all of us that there will be more to come and it can come very quickly," the former assistant director of the Observatory said. "Hailstorms may become more frequent and less sporadic. Look at this one and you find it hit almost everywhere in the city. This was never seen before."
He was speaking as renewed wild weather sent a container toppling from atop a stack into a car park in Tsing Yi, damaging several vehicles.
Director of Drainage Services Daniel Chung Kum-wah said a rainstorm of last night's ferocity occurred only once in 200 years. It had triggered 29 flood reports, of which three were severe, including the one in Festival Walk where water poured into the up-market Kowloon Tong mall. The other two were in Tsuen Wan and Wong Tai Sin.
Chung said the drainage system had the capacity to handle rains of 130 millimetres an hour - the kind of storm that occurred once every 50 years. However, he said in a radio interview: "Rain fell at over 150 millimetres an hour; that happens once in 200 years."
Observatory senior scientific officer Sandy Song Man-kuen said the hailstones on Sunday night were up to 3cm in size, while some as large as 10cm had been reported in 1981.
"It's difficult to relate one hail incident to global climate change but you can see the trend - the air is warmer and holds more moisture, so there is either no rain or extremely heavy rain," she said.
Edwin Lau Che-feng, Friends of the Earth's head of advocacy, said the whole city, not just the government, should review if it was ready for such weather. "What are our contingency measures? Are they effective enough? There is no guarantee we will be so lucky next time," he said.