Hong Kong is preparing for the arrival of typhoon Usagi, which is expected to be the strongest storm to hit the city in more than 30 years.
Officials have suspended activity at the port – one of the world’s busiest – and cancelled most flights.
In mainland China thousands of boats in the Pearl River Delta have been taken inland due to fears of high tides.
At least two people were killed by the storm as it crossed the Luzon Strait between Taiwan and the Philippines.
Typhoo Usagi – which means rabbit in Japanese – packed winds of 103 mph as it closed in on China’s densely populated Pearl River Delta.
China’s National Meteorological Centre has issued its highest alert, warning that Typhoon Usagi would bring gales and downpours to parts of the southern coast, according to Xinhua news agency.
More than 80,000 people have moved to safer ground in Fujian province, Xinhua said, and the authorities in Guangdong have asked more than 44,000 fishing boats to return to port.
Technicians at the Guangdong nuclear plant have been trying to ensure the installation is secure ahead of the typhoon.
Many airlines have cancelled flights to cities in Guangdong and Fujian, and shipping has been suspended between the Chinese mainland and Taiwan, Xinhua reported.
In Hong Kong, meteorologists are warning of severe floods due to powerful winds and exceptionally high tides.
The Hong Kong Observatory warned of “severe” disruption to the city.
If the situation does not improve soon, many businesses including the stock exchange will be shut on Monday.
En route to Hong Kong and southern China, Typhoon Usagi forced the evacuation of more than 3,000 people in southern Taiwan.
It also hit the northernmost islands of the Philippines, where it cut communication and power lines and triggered landslides.
Typhoons are common during the summer in parts of East Asia, where the warm moist air and low pressure conditions enable tropical cyclones to form.