A magnitude 6.1 earthquake has hit Taiwan, with tremors felt in the capital Taipei and across the country.
Taiwan's Central Weather Bureau intially put the magnitude at 7.2, but there were no immediate reports of injuries or significant damage.
The USGS issued an alert on Tuesday morning saying the earthquake's epicentre was around 90km off the coast of Taiwan, at a depth of more than 240km.
There was no immediate alert or advisory from the Pacific Tsunami Warning Center.
But the USGS's initial analysis suggested some 30 million people lived near enough to the earthquake epicentre to experience some shaking.
Witnesses reported tremors felt in major buildings in Taipei, including the national parliament, as well as at the international airport in Taoyuan south of the capital.
There were some concerns for the world's largest contract microchip-maker, Taiwan Semiconductor Manufacturing Inc, located not far from Taipei. The company said there was no impact to its operations.
