The largest fires were in south-eastern regions, including the rural county of Sancheong, where 260 people fled to a temporary shelter as flames spread across the surrounding hills, according to the South Gyeongsang provincial government.
Two firefighters were found dead, while another firefighter and a government worker remain missing after being trapped by fast-moving flames driven by strong winds in the area.
Rescuers pulled out five emergency workers, who are now receiving treatment for their injuries, the provincial government said.
The Korea Forest Service said the Sancheong wildfire had burned more than 1200 acres as of Saturday evening.
Nearly 1600 emergency workers, 35 helicopters and dozens of vehicles were deployed, but only 35 per cent of the blaze was contained due to the area's mountainous terrain and strong winds.
More than 400 people evacuated their homes in the county of Uiseong in North Gyeongsang province as firefighters continued to fight a blaze that so far burned 740 acres, according to the forest service.
Dozens of residents also fled their homes in the city of Gimhae.
The fires forced the closures of several highway sections in the country's south-east, including one connecting Ulsan and Busan, South Korea's second-largest city.
The national government designated the North and South Gyeongsang provinces and the southeastern city of Ulsan as disaster zones, and the country's acting president, Choi Sang-mok, vowed an all-out response to extinguish the flames.
Wildfires were also reported in central Chungcheong and southwestern Jeolla provinces.
