Taiwan has seen 19 earthquakes today, all occurring just off the coast of Hualien, according to the Central Weather Bureau (CWB).
National Central University Institute of Applied Geology professor Lee Chyi-tyi describes this cluster of earthquakes as a "earthquake swarm".
Multiple aftershocks are continuing to strike the area.
The building is reported to be Marshal Hotel in Hualien City, which has about 300 rooms.
Photos below showed extensive damage to roads and high-rise buildings partially collapsed.
Emergency services are working to free people who are trapped, the reports say.
A hotel on the east coast of Taiwan has collapsed after a 6.4-magnitude earthquake, the national fire agency said, with reports that several other buildings have been toppled with some people trapped.
Images on local television showed the Marshal Hotel in Hualien slanted on its side, partially crumpled into the ground.
Media reports said there were 30 people trapped inside with others crawling to safety.
The fire agency said a second hotel had also been damaged, with televison images showing roads strewn with rubble and cracks in highways.
The quake hit at 23:50 pm (1550 GMT) around 21 kilometres (13 miles) northeast of the port city Hualien, according to the United States Geological Survey.
It follows almost 100 smaller tremors to have hit the area in the last three days.