In Taiwan, Japan and the Philippines, officials initially issued tsunami warnings, but by about 10 a.m. (0200 GMT), the Pacific Tsunami Warning Center said the threat had “largely passed”.
In Taiwan's capital, the subway was briefly shut down but restarted within an hour, while residents received warnings from their local town chiefs to check for any gas leaks.
Taiwan is regularly affected by earthquakes because the island is located near the junction of two tectonic plates, while nearby Japan experiences about 1,500 tremors each year.
Across the Taiwan Strait, social media users in China's eastern Fujian province, which borders Guangdong to the south, and elsewhere said they also felt strong tremors.
Hong Kong residents also reported feeling the earthquake.
China, which claims self-ruled Taiwan as a rebel province, was “paying close attention” to the earthquake and was “ready to provide disaster relief assistance,” state news agency Xinhua said.
Construction work at some plants at Taiwan Semiconductor Manufacturing Co, the world's biggest chipmaker, was briefly disrupted, while work at construction sites for new plants was halted for the day, a company official told AFP.
Most earthquakes around the region are mild, although the damage caused by them varies according to the depth of the epicenter and its location below the Earth's surface.