Torrential rain swept across South Korea on Friday, forcing the cancellation of over a hundred flights and leaving thousands of homes without power as the government put officials on high alert for the peak of the summer monsoon season.

Over 4,000 households have experienced power cuts in the capital Seoul due to the heavy rain that began on Sunday with 136 people forced to evacuate nationwide, as of 11 a.m. (0200 GMT), according to the Ministry of Interior and Safety.

Over 130 flights were cancelled at airports across the country on Friday with more than 270 flights delayed as of 5 p.m., according to the Korea Airports Corporation.

One person is missing in the southern city of Busan while one has been injured in South Jeolla Province, officials said.

In a meeting with government agencies, Prime Minister Han Duck-soo said it was of utmost importance that "no casualties were caused" and ordered officials to stay on alert. More than 10,500 police were put on traffic duty and increased patrols.

Last summer, Seoul was hit with floods caused by the heaviest rain in 115 years, inundating basement flats in low-lying neighbourhoods, including in the largely affluent Gangnam district.

North Korea has also been getting heavy rains and might open floodgates at dams on rivers flowing across the border between the two Koreas, Han added.

"Heavy rain is expected in Hwanghae Province and we need to thoroughly prepare for the possibility that North Korea might release water from its Hwanggang Dam," he said, referring to the North's central region.

North Korea's official KCNA news agency reported on Friday many parts of the region had received more than 100 millimetres (4 inches)of rain since Thursday morning but did not say if there was any damage.

Such water releases, often undertaken without notice by Pyongyang, have caused sudden surges of water in rivers that in previous years caused flooding and resulted in deaths in the South.

The Unification Ministry, which handles relations with the North, said on Friday it sent a message last month requesting notice in the event of water release but received no response. (Reporting by Hyunsu Yim; Editing by Conor Humphries)