The KMA said some 20 to 70 mm more rain is forecast, with up to 100 mm in some areas in Seoul, Gyeonggi and Gangwon provinces through the afternoon. Rain is expected to let up around 6 p.m. in most areas, it said.

The KMA issued a heavy rain warning in the country’s northern Gyeonggi Province -- around Paju and Goyang specifically -- at 8:20 a.m. and Seoul and Incheon at 9:20 a.m. At 9:45 a.m., six cities and counties, including Anyang and Suwon in Gyeonggi Province, were added to the list.

As of 11 a.m., the heavy rain warning had been issued in a total 13 cities.

A heavy rain warning is issued when a region receives more than 110 mm of rain in six hours or if more than 180 mm of rain is expected in the next 12 hours.

As of 11 a.m., Goyang received the most rainfall at 148.5 mm per hour, followed by Siheung at 111.5 mm, Paju at 105 mm and Yangju at 104 mm, all in Gyeonggi Province, according to the weather agency. Incheon and Seoul saw 90.5 mm and 88.5 mm of rain, respectively.

The Ministry of Public Safety and Security sent a warning text message for Koreans to refrain from outdoor activities and residents in areas at risk of flooding and landslides to evacuate.

A part of Cheonggye Stream in central Seoul and Jeungsan Bridge in northwestern Seoul were shut down, police said. Traffic was also restricted in parts of Gaehwa-dong, Incheon.

According to Korea Railroad Corp., the state-run railway operator, trains connecting Bupyeong Station and Incheon Station in Incheon at 9:30 a.m. both ways were halted due to an electrical malfunction after a thunderbolt struck rail tracks. 

Train operations between the stations were resumed after 27 minutes.

By Ock Hyun-ju (laeticia.ock@heraldcorp.com)