Mangkhut weakened from a typhoon to a tropical storm as it moved deeper into southern China on Monday, leaving death and destruction from Hong Kong to the Philippines.
The storm was still affecting southern China's coast and the provinces of Guangdong, Guangxi and Hainan and rain and strong winds were expected to continue through Tuesday.
Hong Kong residents were told to stay away from the coastline and be on alert for occasional gales.
Bus, ferry and rail services were suspended and almost 900 flights were cancelled at the city's airport, one of the world's busiest.
The South China Morning Post said Hong Kong's hospitals had to use back-up power due to outages caused by the storm.
Philippine and Chinese authorities said the death toll from a typhoon has risen to at least 69 with dozens missing.
A Philippine national police report said the latest death toll was 65, with 43 people missing and 64 injured. Chinese authorities reported four deaths from falling trees and building materials in Guangdong, China's manufacturing hub.
Many of the missing in the Philippines are gold miners and their families feared buried in a landslide after seeking shelter in a bunkhouse-turned-chapel in a village in Benguet province.
As of Monday morning Mangkhut was on track to pass over the Guangxi regional capital of Nanning and move toward the border with tourism powerhouse Yunnan province.
The Hong Kong Observatory reported Mangkhut was the most powerful cyclone to hit the city since 1979, packing maximum sustained gusts of 121 mph.
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.
"Prepare for the worst," Hong Kong Security Minister John Lee Ka-chiu urged residents.
That warning followed Mangkhut's devastating march through the northern Philippines on Saturday with sustained winds of 127 miles per hour.
Landslides caused by the pounding storm hit two villages in Itogon town in the mountain province of Benguet.
Itogon Mayor Victorio Palangdan told The Associated Press by phone that at the height of the typhoon's onslaught on Saturday afternoon, dozens of people, mostly miners and their families, rushed into an old three-story building in the village of Ucab.
The building - a former mining bunkhouse that had been transformed into a chapel - was obliterated when part of a mountain slope collapsed. Three villagers who managed to escape told authorities what happened.
"They thought they were really safe there," the mayor said on Sunday.
The rescue work halted for the night before resuming on Monday morning.
Men used pikes and shovels to dig into the mud since the soaked ground was unstable and limited the use of heavy equipment on site.
Mangkhut also shattered glass windows on commercial skyscrapers, felled trees, tore scaffolding off buildings under construction and flooded some areas of Hong Kong with waist-high waters, according to the South China Morning Post.
Casinos on Macau were ordered closed for the first time due to the typhoon.