Emergency workers rushed to the scene and used a crane to rescue the pair.
They were taken to a nearby hospital with minor injuries.
City officials and the Korean Geotechnical society are looking into the cause of the sinkhole.
Cho Seong-ha, from the Korean Geotechnical Society said water was coming out of the retaining wall.
“However, it is still not known whether this was the immediate cause of the ground sinking,” Cho Seong-ha said.
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“We are planning to analyse the possibility through investigation. We are also planning to figure out other causes for the sinking by looking at various construction records and by investigating the site."
