The "extremely fierce" blaze started around 3 a.m. on Thursday, engulfing the entire building in the city of Kaohsiung and destroying many floors. Witnesses said they heard an explosion around the same time.
Orange flames lit up the night sky as firefighters worked to cut down the blaze, leaving the building smoldering hours later.
At least 11 bodies were sent straight to the morgue, Fire Chief Li Ching-hsiu told reporters at the scene. Another 14 people who showed no signs of life were among 55 taken to the hospital. In Taiwan, official confirmation of a death can only be made in the hospital.
The cause of the fire is under investigation.
The building is around 40 years old.
The Associated Press contributed to this report.