The National Fire Agency said that from the injured, 2 dozen are in critical condition.
Three buildings have collapsed, including the Marshal Hotel in Hualien City.
Hualien is a popular tourist destination on Taiwan's eastern coast and home to about 100,000 people.
The Ministry of Foreign Affairs and Trade said it had received no requests for consular assistance following the quake.
A Reuters video showed large cracks in the road, while police and emergency services tried to help anxious people roaming the streets.
Several lower magnitude tremors followed the main quake. On Sunday, a 6.1-magnitude temblor struck nearby.
The natural disaster, which struck at 11:50 p.m. local time on Tuesday, was centered in the water about 18 kilometers (11 miles) northeast of Hualian, or 98 kilometers (61 miles) east of Taichung City.
Taiwan's government launched an emergency recovery operation. But most residents got out and authorities said they believed no more people were trapped inside.
It followed nearly 100 smaller tremors to have hit the area in the last three days and comes exactly two years since a quake of the same magnitude struck the southern Taiwanese city of Tainan, killing more than 100 people. By 3 p.m. today, the amount has surpassed 153 and 18 of those were substantial enough to be felt, reported CNA.
Rescuers worked Wednesday to free people trapped after a strong quake near Taiwan's east coast caused several buildings to cave in and tilt dangerously.
Among the injured were two Japanese, though a Japanese official said Wednesday they are not in a life-threatening condition.
A maintenance worker who was rescued after being trapped in the Marshal Hotel's basement said the force of the natural disaster was unusual.
The government said 214 people had been injured. While most of the unaccounted for were likely to be in one residential building, the agency did not have an estimate of how many were in the building at the time.
Sections of the Suhua Highway connecting Ilan and Hualien counties were severely damaged.
A magnitude-6.4 quake has rocked Taiwan's east coast, following a "swarm" of 19 earthquakes over the past 48 hours.
With aftershocks continuing through the night, residents were being directed to shelters, including a newly built baseball stadium, where beds and hot food were provided.
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