People cool down under the shade in Jongno District, Seoul, Sept. 10. Yonhap

An unprecedented autumn heat wave is set to reach its peak on Wednesday, the state weather agency said, as the daytime high is forecast to rise to a record 35 degrees Celsius in Seoul amid a heat wave advisory issued for almost all regions of the country.

The Korea Meteorological Administration (KMA) said overnight temperatures in the capital again stayed above 25 degrees on Tuesday, marking the latest tropical night since modern meteorological observation began. The southern island of Jeju experienced the tropical night phenomenon for a record 65 consecutive days.

The maximum daily temperature in Seoul is expected to soar to 35 degrees, which will set a new record for the highest temperature of September, the KMA said.

The agency issued a heat wave advisory for almost all regions, excluding east coast areas of Gangwon Province, inland areas of North Gyeongsang Province and Jeju's Mount Halla. A heat wave advisory is issued when the highest apparent temperature is expected to be 33 degrees or higher for two or more consecutive days.

The KMA said the ongoing heat wave is expected to abate temporarily for the rest of the week, as rain is expected nationwide on Thursday and in the capital and northern Gangwon regions on Friday. (Yonhap)