"The average temperature from June 1 through Aug. 31 was 25.7 degrees Celsius, the highest since data collection began in 1973," the Korea Meteorological Administration said in a press release.

The previous record over the same period was 25.6C.

South and North Korea also experienced their warmest June, with temperatures in both countries 2C higher.

The number of heatwave days -- when the daily temperature is 33C or more -- over the three-month period was 28.1, the third-highest figure since 1973, the official data showed.

It comes as the country is grappling with a prolonged drought that has hit the eastern coastal city of Gangneung.

A state of national disaster has been declared in the city of 200,000 after weeks without rain -- with water levels at the Obong reservoir, the city's main source of piped water, falling below 15 percent.

The dry spell has forced authorities to implement water restrictions, including shutting off 75 percent of household meters.