At least 24 people have been killed as multiple wildfires continue to ravage South Korea's south-east region.

Most of the victims are in their 60s and 70s, say authorities, adding that some 26 people are injured - with 12 in critical condition - as the deadly wildfires have forced more than 23,000 people to flee their homes.

The "unprecedented" crisis remains critical and is "rewriting the record books for the worst wildfires in our nation's history", said acting president Han Duck-soo.

The fires gutted the 1,300-year-old Gounsa temple in Uiseong city, where many cultural relics were removed and transported to safer ground.

The fires started in Sancheong county on Friday afternoon and later spread to Uiseong county, authorities said.

Fuelled by strong and dry winds, the fires are advancing to the neighbouring counties of Andong, Cheongsong, Yeongyang and Yeongdeok, Yonhap news agency reported.

The Uiseong blaze is spreading at an "unimaginable" scale and speed, Lee Byung-doo, a forest disaster expert at the National Institute of Forest Science, told Reuters.

A firefighting helicopter crashed in the mountains of Uiseong county just after midday on Wednesday, according to authorities, who are investigating the cause.

Thousands of firefighters and about 5,000 military personnel have been deployed to contain multiple blazes, as well as helicopters from the US military stationed in Korea.

'It was like the apocalypse'

On Tuesday, the national fire agency said it had raised the crisis to the highest fire response level, the first time this year such an alert has been issued.

Wildfires are relatively uncommon in South Korea, and related fatalities are rare. The current fires, which have killed 18 people within the past few days, are already the deadliest in the country's history.

About 17,000 hectares (42,000 acres) of forest have also been destroyed, making the fires the third largest in South Korea's history in terms of area.

The blazes raging in the city of Uiseong burned down the Gounsa temple, built in 618 AD, which was one of the largest temples in the province.

A Buddhist architectural structure deemed a national treasure from the Joseon Dynasty (1392-1910) was also destroyed, forestry authorities confirmed.

A 68-year-old monk said he was "devastated" when he heard that about the destruction of the Gounsa temple.

"We will do our best to restore the function of the temple."

"It was an extremely painful feeling, and I wondered why something like this could happen," Joung-ou told news agency AFP.

In Andong, truck driver Lee Seung-joo said he saw the mountains burn like "literal hell" as he drove by.

"It was like the apocalypse," the 39-year-old said, according to an AFP report.

Elsewewhere in Andong, evacuees who were sheltering at an elementary school were told to leave quickly as the fire was spread by gusty winds.

"The wind was so strong," said 79-year-old Kwon So-han told AFP. "The fire came from the mountain and fell on my house."