15-floor office building in Gangnam, Seoul, was evacuated and left vacant Wednesday after signs of its impending collapse were reported the day before. City officials who inspected the building concluded that it was dangerous.

Seoul’s Gangnam District Office designated the Daejong Building in Samseong-dong, Gangnam, as a “Class-3 Establishment,” the lowest safety level, meaning that it presents a “high risk of disaster” or requires “continuous management to prevent disasters.”

Wide cracks on walls and pillars were reported on Tuesday, and a team of inspectors from the Seoul Metropolitan Government conducted a safety check. The cracks were visible on the second floor of the building, where remodeling work was underway, according to the city officials.

After the preliminary inspection, the city officials concluded that the center column of the building had sustained damage of more than 20 percent and the reinforcing steel inside the columns had structural problems.

On Wednesday morning, the Gangnam District Office conducted a second safety check and ordered the occupants to evacuate. The authorities can prevent residents from using buildings classified as Class-3 establishments, and can even order their demolition.

“According to inspectors, we should empty the building in case of an accident during an overhaul planned, and take follow-up measures,” Jeong Yoo-seung, the vice chief of the district office said in a press conference.”

The 14,799-square-meter Daejong Building was built in 1991 and has 15 floors above ground and seven floors below ground. Its 98 occupants include law firms and shops, according to the authorities.

Seoul Mayor Park Won-soon visited the site late Tuesday and ordered the authorities to take immediate action. On Facebook, he posted pictures of the cracked walls.

“Accidents come with prior symptoms. So it is important for all facilities to have a reporting system people can use anytime,” Park wrote. “I ordered an immediate safety inspection to decide (whether to demolish) the building, to provide detailed explanations to the building occupants and to ask them to evacuate.”

By Jo He-rim (herim@heraldcorp.com)