At least 29 people were killed when Mangkhut blitzed the Philippines, leaving devastation in its wake.
In Hong Kong, more than 100 people have been reported injured as the mammoth storm made landfall.
Mangkhut, the strongest storm across the globe so far this year, is packing winds of more than 110 mph, equivalent to a Category 2 hurricane in the Atlantic.
The typhoon has prompted authorities in China to issue the highest alert, warning residents to stay indoors at all costs.
In Hong Kong, there have been reports of skyscrapers swinging and windows being blown out by the force of Mangkhut.
Water levels surged by almost 3.5 m in places and live fish were washed on to the streets.
Most shops and public services were shut, and more than 800 flights have been cancelled at Hong Kong International Airport.
Thousands of people have been evacuated from Guangdong, on the Chinese mainland, where Mangkhut is due to strike later on Sunday.
Resident Martin Wong said: «It’s the worst I’ve seen. I’ve not seen the roads flood like this and the windows shake like this before.»
Mangkhut’s northwesterly track will bring heavy rain and winds to the autonomous region of Guangxi early on Monday, before it weakens into a tropical depression to reach southwestern Yunnan next day.
How bad has the Philippines been hit?
The death toll, officially at 29, is expected to climb as the worst of the damage in rural areas is yet to be assessed.
Most of the deaths have been caused by landslides, officials have reported.
Among the dead are a baby and a toddler.
Blocked roads and downed communications lines mean reports are still coming in.
Five million people were in the path of Mangkhut as it blazed through, with more than 100,000 sheltering in emergency centres.
There is also concern over the economic cost of the typhoon, which has caused extensive damage to farmland in Cagayan, a key agricultural province.
Francis Tolentino, a political adviser to President Rodrigo Duterte, told the BBC that he estimated only a fifth of produce there had been harvested in advance — threatening staples like rice and corn.
The Philippines is routinely hit during the typhoon season but the strength of Manghukt has brought back horrific memories of the deadliest storm on national record — Super Typhoon Haiyan — which killed more than 7,000 in 2013.
However, preparation and evacuation procedures have been improved since then, with warnings issued, travel restricted, schools shut and the army on standby.