More than 2.4 million people had been relocated in southern China's Guangdong province by Sunday evening (local time) to flee the massive typhoon, and almost 50,000 fishing boats were called back to port, state media reported.
Hong Kong's famed Victoria Harbor was also hit with a storm surge of more than 3.9 meters (12.8 feet) above chart datum on Sunday.
Residents hunkered down in their apartments, and streets in the usually buzzing city were deserted Sunday.
Videos and photographs show windows of some of the city's commercial skyscrapers smashed in the high winds.
Low-lying areas, including Lei Yue Mun, Heng Fa Chuen in Chai Wan, and Tai O were seriously flooded, and some people who live in tall residential towers claimed they could feel their buildings shaking. A red alert remained in effect for parts of southern China, where the typhoon was moving westward.
A park is flooded by seawater after Typhoon Mangkhut hit Hong Kong, China, Sept. 17, 2018. The storm had maximum sustained gusts of 195 km/h in the city.
Power utility CLP said access to numerous affected areas was blocked by fallen trees and debris, making fix work extremely hard. Hong Kong authorities say 284 people have sought treatment for minor injuries at hospitals.
On Sunday, Mangkhut moved northwest to China, where it brought heavy rain and strong winds to several southern provinces.
More than 2.4 million people had been evacuated in southern China's Guangdong province by Sunday evening to flee the typhoon, state media said.
Along the coast, the gambling enclave of Macau closed all its casinos, and all fishing boats from China's Guangdong province were called into port. At least 40 people - possibly miners and their families - are believed buried under thick mud caused by nonstop rains last weekend.
Nearly all flights in and out of Hong Kong were canceled. Airlines were expected to resume operations on Monday, but authorities have warned that it would take more than a day to clear the backlog of the some 800 canceled flights. Reuters reports that the government said the storm destroyed rice and corn crops worth an estimated $177 million.
And though the Government had begun clean-up efforts, aid agencies were struggling to reach affected areas, according to Aprilynn Villamar, an emergency program officer for Catholic Relief Services in Benguet.
MTR Corp, the city's sole rail operator, revealed that a number of ground sections of its service lines were affected by fallen trees and objects.
Still, the destruction and death toll was far lower than feared - especially compared to Typhoon Haiyan, which struck the archipelago in 2013, killing at least 6,300 in one of the worst tropical cyclones ever recorded. Such mines can weaken hillsides, increasing the chance of landslides, they said.
Mangkhut has swept over Hong Kong and Macau and on into China's southeast province of Guangdong, after devastating the Philippines, where the toll is likely to surpass 50.
Philippine National Police Director General Oscar Albayalde told The Associated Press that 20 people died in the Cordillera mountain region, four in nearby Nueva Vizcaya province and another outside of the two regions.