Hong Kong reported 158.1mm of rainfall in the space of an hour on Thursday evening, the highest since records began in 1884, causing widespread flooding and disrupting road and rail traffic.
The record rain, reported through midnight Thursday, comes just days after the city avoided major damage from a super typhoon.
On Thursday evening, authorities in the Chinese city said several neighborhoods had been flooded and emergency services were carrying out rescue operations. Members of the public have been asked to stay in a safe place.
“Heavy rains will cause flash floods,” warns the observatory. “Residents living near rivers should remain alert to weather conditions and consider evacuating” if their home is flooded.
No injuries were reported in the early hours of Friday.
Earlier in the week, Typhoon Haikui left a trail of destruction in Taiwan before crossing the strait and making landfall in China’s Fujian province on Tuesday.
The Hong Kong Observatory said the latest torrential rains were caused by the “low pressure trough associated with the rest of Haikui”.
The city’s Mass Transit Railway has announced it will partially suspend service on one of its lines after a station in the Wong Tai Sin district flooded, and a handful of other stations were also affected. .
Other video clips showed half-submerged cars and buses on major roads.
Heavy rain was also reported in the nearby Chinese technology hub of Shenzhen. The city has prepared to drain water from its reservoirs, Hong Kong officials say, which could lead to flooding in parts of northern Hong Kong.
Southern China was hit the previous weekend by two typhoons in quick succession – Saola and Haikui – although Hong Kong avoided a feared direct hit.
Tens of millions of people in densely populated coastal areas of southern China had sheltered in their homes before the storms.
Climate change has increased the intensity of tropical storms, with more rain and stronger gusts causing flash flooding and coastal damage, experts say.