Directly across the line, experts in China's tech center point Shenzhen recorded the heaviest downpours since records started in 1952.
Environmental change has expanded the power of hurricanes, specialists say, with additional downpour and more grounded blasts prompting streak floods and beach front harm.
The heavy rains in Hong Kong began on Thursday, and the city's weather observatory recorded the highest hourly rainfall since records began in 1884 at its headquarters in the hour leading up to midnight.
Flash flood warnings were issued by authorities, and rescue efforts were carried out by emergency services in some areas of the territory.
According to the observatory, "residents living in close proximity to rivers should remain alert to weather conditions and should consider evacuation" in the event that their homes flood.
It additionally cautioned of possible landslips, telling drivers to "avoid steep inclines or holding walls".
Taxis struggled through flooded roads on Friday morning as workers tried to get to work.
The downpour stranded some automobiles.
On the island of Lantau, where rivers overflowed their banks, roads were submerged as well.
Two typhoons—Saola and Haikui—hit Southern China the weekend before, but Hong Kong escaped the anticipated direct hit.
In advance of those storms, tens of millions of people in the densely populated coastal regions of southern China had taken shelter inside.
According to the weather observatory in Hong Kong, the "trough of low pressure associated with (the) remnant of Haikui" was the source of the most recent torrential downpour.
Although there were no reports of injuries, schools were closed and cargo clearance services on the city's border with Shenzhen were halted by the authorities.
The disruption at the border occurred just hours after Hong Kong officials said that Shenzhen was getting ready to release water from its reservoir, which could cause flooding in the northern parts of the city.
After a station in the Wong Tai Sin district was flooded, the operator of Hong Kong's metro system reported a service disruption on one of its lines.
The rain also had an impact on a few other stations.
A video that was shared on social media showed a subway train not stopping at the flood-damaged Wong Tai Sin station.