Parts of Gyeonggi Province, east of Seoul, received more than 220 millimeters of rain per hour from Saturday to 6:00 a.m. on Monday, according to the Korea Meteorological Administration (KMA).
The downpour also pounded Cheorwon in Gangwon Province, a border county far northeast of the capital, with an hourly record of 220.5 mm and Hwacheon in the same province with 150.5 mm.
Central Seoul received some 134.5 mm of rain per hour, with parts of Incheon recording as much as 110 mm per hour, the KMA said.
The heavy rain claimed the life of a man in his 90s living in Incheon on Sunday, the police said. He, who was suffering from Alzheimer's, couldn't make his way out of his house when it was being flooded as he was physically compromised.
A 55-year-old woman in Gangwon was found dead later that day after being swept away by strong currents in the stream near where she had come to visit her friend. Seven construction workers were rescued from a railway site in Incheon after they were isolated about 150-300 meters underground for about an hour.
A total of 2,345 houses in Incheon alone suffered damage from flooding caused by the heavy rain, with parts of Gyeonggi also depriving at least 76 residents of homes. In Gyeonggi Province, more than 140,000 houses experienced a short blackout.
The weather authorities forecast the country will receive up to another 80 mm of rain in the southern regions until late Tuesday, advising caution for any damaged areas. The rest of the country is projected to record 40-60 mm of more rain, it added.