The storm hit the city of Taishan in China’s coastal Guangdong province at 5pm local time, triggering storm surges as high as 3 metres, according to China’s state broadcaster CCTV.
Nearly 50,000 fishing boats have been called back to port by authorities and more than 2.4 million people have been evacuated from the seven cities in the province.
China’s national meteorological centre said that the country’s southern region faced a “severe test caused by wind and rain”.
Officials from the centre also urged authorities to prepare for possible disasters.
A red alert, the most severe warning in such circumstances, has been issued by authorities in southern China.
The storm has broken windows, felled trees and torn bamboo scaffolding off buildings, according to the South China Morning Post.
Transport in the region has ground to a halt, with all high-speed rail services in the Guangdong and Hainan provinces suspended and hundreds of flights cancelled.
The storm’s winds had weakened slightly to 95mph on Sunday morning, with gusts of up to 120mph.
The Hong Kong Observatory said that even with slightly less momentum Typhoon Mankhut’s intense rainbands were still bringing heavy downfall and frequent squalls to the region.
The typhoon brought storm surges of 3 metres around Hong Kong and the city’s RTHK broadcaster cited experts as saying that the typhoon is expected to be the strongest that has hit the city in decades.
15 people have been injured in Macau, which borders Hong Kong.
“Because Mangkhut will bring winds and rains of extraordinary speeds, scope and severity, our preparation and response efforts will be greater than in the past,” Hong Kong Security Minister John Lee Ka-chiu said.
“Each department must have a sense of crisis, make a comprehensive assessment and plan, and prepare for the worst.”
Hong Kong’s Cathay Pacific said all its flights would be cancelled between 2.30am Sunday and 4am Monday. The city of Shenzhen also cancelled all flights between Sunday and early Monday morning.
Associated Press contributed to this report