The bus, which was stationary at the time on a busy road, was buried under the rubble in Gwangju, alcuni 270 chilometri (168 miglia) southwest of the capital, Seoul.
A further 25 persone sono rimaste ferite, including eight seriously, the ministry added.
Il 16 demolition workers on the site are safe and did not sustain any injuries as the building collapsed.
Approximately 190 firefighters were deployed for search and rescue, and police joined the rescue effort, the ministry said.
The reason for the collapse was unclear, Reuters ha riferito, citing officials at the Gwangju Fire and Safety Headquarters. The Ministry of Land, Infrastructure and Transport will investigate the cause of the collapse.
South Korea has struggled with a bad safety record of infrastructure — a department store collapse killed more than 500 persone in 1995, and a bridge collapse in 1994 ucciso 49 persone. In anni recenti, the country has tried to improve its safety record.