The typhoon, the biggest to hit China's eastern seaboard in 2024, cross the coast on Thursday night in Fujian province, state broadcaster CCTV said.
The storm is forecast to unleash intense rainfall over much of China after fuelling severe weather from the Philippines to Japan's Okinawa islands with its giant cloud-bands that spanned most of the western Pacific Ocean.
In Taiwan, the strongest typhoon to hit the island in eight years packed gusts of up to 227km/h before weakening as it made its way across the island, according to the Central Weather Administration.
Some parts of southern Taiwan are expected to have recorded accumulated rainfall of 2200 millimetres since Tuesday.
Parts of southern Taiwan are expected to have recorded accumulated 2200mm of rain since Tuesday. (AP PHOTO)
The storm cut power to around half a million households, though most are now back online, utility Taipower said.
Chinese weather forecasters predict Gaemi will pass through Fujian and head inland, gradually moving northward with less intensity.
But weather forecasters are expecting heavy rain in many areas as it tracks north.
Three people died and 380 were injured by the typhoon in Taiwan, the government said, as the storm made its way across the island.
A Tanzania-flagged freighter with nine Myanmar nationals on board had sunk off the coast of the southern port city of Kaohsiung and there had been no response from the crew.
Search efforts were ongoing, Taiwan's fire department said.
Four other ships ran aground in the storm, including an Indonesia-flagged cement vessel that hit the shore near the southern town of Fangshan.
All crew members were safe, authorities said.
Taiwanese television stations showed pictures of flooded streets in cities and counties across the island.
Offices and schools as well as the financial markets closed for a second day on Thursday, while trains were stopped until midafternoon and all domestic flights and 195 international flights were cancelled.
An Indonesia-flagged cement ship ran aground due to Typhoon Gaemi in southern Taiwan. (EPA PHOTO)
Before Gaemi's arrival, China's governing Communist Party's top decision-making body held a meeting to discuss flood prevention and disaster relief, state media said, while the transport ministry upgraded its typhoon response to level two.
Local officials also stepped up warnings in the coastal provinces of Fujian and Zhejiang.
In Fujian, government officials have relocated about 150,000 people, mainly from coastal fishing communities, state media reported. As gale force winds picked up, officials in Zhoushan in Zhejiang suspended passenger waterway routes for up to three days.
Most flights were cancelled at airports in Fuzhou and Quanzhou in Fujian, and Wenzhou in Zhejiang, according to the VariFlight app.
Guangzhou rail officials suspended some trains that pass through typhoon-affected areas, according to CCTV.
Meanwhile, other part of China experienced heavy rain from summer storms around a separate weather system.
Torrential rain has caused mudslides in China's southwest Sichuan province, leading to the evacuation of 288 people from a popular scenic spot, according to state media.
Further north, some areas in Beijing also experienced heavy rain and emergency plans were activated, with more than 25,000 people evacuated, according to Beijing Daily.
