The typhoon, which is expected to have maximum speeds of 130 miles per hour is predicted to be closest to the financial hub at around midnight, forcing workers to stay at home and trading on the stock market to be suspended.
Around 460 flights have been in the key travel hub.
Rail authorities in mainland China suspended all trains entering or leaving Guangdong province from Friday night to Saturday evening over the typhoon, state media reported.
The Hong Kong Observatory issued a Number 9 storm signal, the second-highest warning under the city’s weather warning system.
The observatory’s director, Chan Pak-wai, said the alert could yet be upgraded to a Number 10 signal, the first such warning since Super Typhoon Mangkhut hit Hong Kong in 2018.
The observatory warned of serious flooding in coastal areas and said the maximum water level might be similar to when Mangkhut felled trees and tore scaffolding off buildings in the city.
Around 280 people sought refuge at temporary shelters as the city braced for strong winds and heavy rains and ferry and bus services were halted.
Residents of low-lying areas placed sandbags at their doors to prevent their homes from being flooded.
Two men were injured and sought treatment at public hospitals and classes at all schools will remain suspended on Saturday.
Weather authorities in the nearby gambling hub of Macau also warned of flooding, forecasting that water levels might reach five feet in low-lying areas Saturday morning.
In recent months, China has experienced some of its heaviest rains and deadliest flooding in years in various regions, with scores killed, including in outlying mountainous parts of the capital, Beijing.
In the technology hub of Shenzhen, officials ordered a suspension of work, businesses and public transport with the typhoon expected to hit the city or nearby areas on Friday night.
Use of highways in the city was banned except for rescue crews.
China’s National Meteorological Center said Saola could make landfall from Huidong County to Taishan city in Guangdong province, which neighbours Hong Kong, between Friday night and Saturday morning.
It said the storm could also move west near central Guangdong.
Another storm, Haikui, was also gradually moving toward eastern China, meaning parts of Guangdong, Fujian and Zhejiang provinces will experience strong winds and heavy rains, the meteorological administration said.