The Hong Kong Observatory (HKO) raised the storm signal to T10, closing shops and suspending transport as residents were warned to stay inside and well away from the water's edge, reports CNN.
Mangkhut is already the storm of 2018, and is currently packing sustained winds of 165 km, with gusts up to 205 km per hour.
On Saturday, it plowed into the Philippines, killing at least two people and flattening homes in small towns and villages on the northern island of Luzon.
Mangkhut is now some 220 km south-southeast of the city, and heading for the surrounding Pearl River Delta, home to 120 million people.
The storm is expected to be one for Hong Kong's record books. It's only the 15th time in the last 60 years that a T10 alert has been hoisted; the last was for super typhoon Hato last year.
The city's famed Victoria Harbour is expected to see a storm surge of 3.5 metres later on Sunday.
Hundreds of flights from the city's airports were delayed or cancelled, and much of the city's public transport has been suspended.
The storm is currently moving 30 km per hour toward the coast of China's Guangdong, CNN quoted the HKO as saying.
It's expected to pass about 100 km south of the Pearl River Delta -- an area in southern China that includes the cities of Hong Kong, Guangzhou, Shenzhen, Zhuhai and Macau -- on Sunday afternoon, according to the the HKO.
However, the storm has weakened and is now classified by the HKO as a severe typhoon rather than a super typhoon. But officials in Hong Kong are still warning residents to be cautious.
Mangkhut is expected to make another landfall late Sunday night, hitting the Chinese province of Guandong near the cities of Yangjiang and Zhanjiang.
From there the system will continue to move westward and will rain itself out over northern Vietnam, which could lead to some flooding there early next week.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
