An earthquake with a magnitude of 6.6 struck off the coast of Taiwan early Wednesday, the US Geological Survey said.
There were no immediate reports of fatalities or injuries, or major damage.
The USGS said the quake, which it downgraded from an earlier estimate of magnitude 6.9, had a depth of 10 kilometres (six miles) and hit 70 kilometres south of Hualien City.
An AFP reporter felt her building shaking a few minutes after 1:40 am (1740 GMT) in Taipei's Zhongshan district. Government-issued alerts sent people's cell phones blaring.
Taiwan's Central Weather Bureau said an initial quake of 5.4-magnitude at occurred at 1:06 am.
It was followed by the big one of magnitude 6.6 at 1:41 am, and two minutes later came a 6.1-magnitude aftershock, the bureau reported.
Taiwan is regularly hit by earthquakes as the island lies near the junction of two tectonic plates.
Taiwan does not issue tsunami warnings unless a quake is more than magnitude 7.0.
Some earthquakes of 6.0 or more can prove deadly, although much depends on where the quake strikes and at what depth.
But the USGS gave a "green" ranking to the threat posed by the latest quake, predicting a low likelihood of either casualties or damage.
The last time Taiwan experienced a quake of a similar magnitude was in January, when a 6.2 quake hit its east coast. But there were no reports of widespread damage or injuries.
A 6.5-magnitude quake struck northeastern Yilan in October 2021 with minimal damage.
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There were no immediate reports of serious structural damage to buildings, but power was out in some areas of the city and people were fleeing to higher ground