The powerful typhoon has battered the country's southern coast with huge waves and heavy rain, leaving thousands displaced.
In the port city of Pohang, at least six bodies were pulled out of the car park of an apartment complex, the Central Disaster and Safety Countermeasures Headquarters said.
But rescue workers dragged two survivors out of the flooded underground garage on stretchers as residents cheered.
A man aged in his 30s was found alive clinging to pipes, while a woman in her 50s had climbed on top of construction panels. Both had been able to breathe because of a pocket of air in the flooded underground space, fire official Park Chi-min told a televised briefing from the hard-hit city.
The two were now in a stable condition, he said.
A woman in her 70s died in Pohang after being swept away by floodwaters on Tuesday, reports said.
More than 170 members of local fire stations, the military and the coast guard joined forces in the rescue efforts, wading through metres of muddy water to find survivors, he said.
The typhoon forced more than 4,700 people to flee their homes for safety, destroying around 12,000 homes and buildings.
Nearly 90,000 households lost power nationwide as the storm hit, but supply had been restored to most of them by Wednesday morning, authorities said.
Before the typhoon made landfall, South Korean authorities closed more than 600 schools nationwide as a precaution and local airlines cancelled some 250 domestic flights.
President Yoon Suk-yeol offered condolences to the bereaved families and promised support for all rescue operations and typhoon victims.
Mr Yoon called for designating Pohang as a special disaster zone eligible for tax breaks and government subsidies. He travelled to the area later on Wednesday.