Packing winds of more than 200 kph, tropical cyclone Mangkhut is considered the strongest to hit the region this year, equivalent to a maximum Category 5 "intense hurricane" in the Atlantic.
That's more powerful than the maximum sustained winds of 150 kph when Hurricane Florence roared into North Carolina in the United States on Friday.
The eye of Mangkhut, the Thai name for Southeast Asia's mangosteen fruit, skirted 100 kms south of Hong Kong but the former British colony was still caught in the typhoon's swirling bands of rain and gale-force winds.
Hong Kong raised its highest No. 10 typhoon signal at mid-morning as ferocious winds uprooted trees and smashed windows in office and residential buildings, some of which swayed in the gusts, residents said.
Water levels surged 3.5 m in some places, waves swamped roads and washed up live fish, washing into some residential blocks and a mall in an eastern district.
The plans of tens of thousands of travellers were disrupted by flight cancellations at Hong Kong's international airport, a major regional hub. Airlines such as flagship carrier Cathay Pacific cancelled many flights last week.
In the Philippines, casualties reported by various agencies on Sunday evening indicate the death toll from the impact of Mangkhut could exceed 50, with most killed in landslides in or near mountainous areas of the Cordillera region.