Hundreds of residents were evacuated from the high-rise building in the South Korean port city, authorities said.
Hundreds were forced to evacuate and more than 80 people were sent to hospital for smoke inhalation.
The fire reportedly started at around 11.07pm local time (around 3:07pm GMT).
According to the local news site, the fire spread through the building spurred on by the strong winds now in force in the area. Strong winds helped spread it further up.
One eyewitness told Yonhap: "Suddenly, the fire came up".
The fire jumped to a neighboring shopping centre but flames there were quickly controlled.
European Union regulator starts review of BioNTech-Pfizer vaccine
More than 28,000 have recently received their second shot, the statement said. Its goal is to develop vaccine development , production and reach everyone.
DON'T MISS North Korea cover-up: Fury as Kim Jong-un issues dire punishment [UPDATE]North Korea threatens escalation in tensions amid body search [INSIGHT]Get OUT! It was not immediately clear if there were any deaths or serious injuries.
Witnesses said that the exterior walls of the building, possibly insulation, appear to have caused the fire to spread quickly.
The building has not been completely extinguished due to the heat and embers being flared by the winds.
The cause of the fire has not yet been identified although an investigation has been initiated.
Social media footage shows the middle of the apartment tower smoulder with smoke the morning after the incident.
Ulsan is a city in the south-east of the country with a population of 1.2 million people.