Heavy rains turned the streets into rivers, submerging vehicles and overwhelming public transport systems. [Photo: ABC News]

At least seven people have died in and around South Korea’s capital Seoul after torrential rain knocked out power and left roads and subways submerged.

The city’s southern part received more than 100 millimetres of rain per hour late on Monday, according to local media citing the Korea Meteorological Administration (KMA).

Hourly totals in some areas passed 140mm, the worst rainfall in 80 years.

Commuters were slowly returning to work Tuesday morning after emergency crews worked overnight to clean up much of the mess.

But there were concerns about further damage as torrential rain was forecast for the second day in a row.

While most of the Seoul metropolitan area’s subway services were back to normal operations, around 80 roads and dozens of riverside parking lots remained closed due to safety concerns.

In the glitzy, highly concentrated Gangnam district, some buildings were without power and had been inundated, while cars, buses and subway stations were submerged, leaving people stranded. Some stores had also been under water.

At least five people died in Seoul and two others in the neighbouring Gyeonggi province, the Central Disaster and Safety Countermeasures Headquarters said.

Four died after being trapped in flooded buildings, one was electrocuted, one person was found under the wreckage of a bus stop, and another died in a landslide, it said.

At least nine people were injured, while six people remained missing.