The super typhoon, with gusts of up to 227km/h (141 mph), killed one person and left half a million homes without power in Taiwan.
It made landfall near China's south-eastern city of Xiamen on Thursday morning, having lost some power.
Dozens of flights and train services in southern China have been cancelled and tens of thousands of people evacuated.
"It is the strongest typhoon to hit Taiwan in 21 years in terms of maximum sustained wind near the centre," forecaster Hsieh Pei-yun told news agency AFP.
The typhoon has made landfall at the start of a three-day holiday in China for the Mid-Autumn Festival.
Residents were told to stay indoors and ships ordered to head back to harbour, while people in Pingtung were told to leave their homes.
In Taiwan, one person was killed and 38 were injured, said officials.
The storm prompted warnings about possible landslides in mountainous areas - 800mm of rain had been forecast in some areas.
Schools and offices were closed in most eastern and southern counties, while power cuts affected 650,000 households.
Electricity poles and trees were uprooted by winds, with trucks overturned and roofs blown off.
Taiwan is often hit by powerful storms, with super typhoon Dujuan killing three people and leaving more than 300 injured in Taiwan in 2015
Three people were killed and hundreds injured in July when typhoon Nepartak hit Taiwan's east coast.
Another typhoon, Malakas, is expected to approach Taiwan on Friday and Saturday, but is unlikely to make landfall.
Typhoon Meranti has landed in mainland China after battering Taiwan with its strongest storm in 21 years.