The tremor struck at 9:08 am (0108 GMT) 49 kilometres (30 miles) southeast of Taitung at a depth of five kilometres (three miles), the US Geological Survey said.
The epicentre was about 135 kilometres (84 miles) southeast of Taiwan's capital Taipei.
The island of Taiwan lies near the junction of two tectonic plates and is regularly hit by earthquakes.
In September 1999, a 7.6-magnitude tremor killed around 2,400 people in the deadliest natural disaster in Taiwan's recent history.
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