Wildfires in South Korea have doubled in size within a day, becoming the worst natural fire disaster the country has ever experienced, with at least 26 people killed and historic temples reduced to ashes.

The fires have engulfed more than 33,000 hectares (81,500 acres) in the central Uiseong county, marking the largest single forest fire in South Korea’s history.

According to the acting president, Han Duck-soo, the rapid spread of the forest fires has led to a critical situation with numerous casualties.

The military has supplied aviation fuel to keep firefighting helicopters in operation, and more than 9,000 people and 120 helicopters are currently being mobilized to combat the fires.

The wildfires, which have been burning for nearly a week, have destroyed more forest than any previous fire in South Korea.

The fatalities include a helicopter pilot and four firefighters who died after being trapped by fast-moving flames driven by strong winds.

Authorities suspect human error as the cause of several wildfires, including cases where people started fires while clearing grass or during welding work.

The fires are threatening two Unesco world heritage sites and have led to evacuations in affected areas, including villages and mountainous regions.

Forecasted rain is expected to be minimal, of little help in extinguishing the fires.

Firefighters had previously managed to put out most of the flames in key areas, but winds and dry conditions allowed the wildfires to spread again.

Historic structures, including temples, have been destroyed in the blazes.

The Korea Forest Service has raised its wildfire warning to the highest level and implemented measures to prevent further spread.

Climate change is expected to contribute to more frequent and deadly wildfires globally.

Reporting by Reuters, Associated Press and Agence France-Presse