Why have the wildfires in S Korea been so devastating?

Strong winds, dense forest and unusually dry weather - that's the deadly combination that experts say is fuelling the largest wildfires in South Korea's history.

The inferno in the south-east has burned through 35,810 hectares (88,500 acres) as of Thursday - that's about half the size of New York City - killing 27 people so far and displacing tens of thousands.

Authorities believe the wildfires started by accident from human activity, but the main drivers of the devastation are dry land, and strong gusts sweeping over inland regions.

The high concentration of pine forest in North Gyeongsang province, where the fires are burning, is also "oiling" the blaze, said a forest disaster expert.

Andong, one of the worst-hit cities, is known for its tranquil pine forests.

While they provide shelter and food for local wildlife and sometimes help break the wind, pine trees "become problematic during wildfires", Mr Lee told the BBC.

"Because forests [in South Korea] contain large numbers of pine trees, the areas are particularly vulnerable when fires break out," he said.

Furthermore, pine trees retain their needles throughout winter, making them susceptible to "crown fires" - wildfires that spread by igniting the dense canopy of branches and leaves. This has contributed to the rapid and extensive spread of the flames over the past week.

Unlike neighbouring countries such as China and North Korea, South Korea has made gains in forest cover over recent years.

"Most mountains are now filled with fallen leaves and pine trees... This accumulation has become a significant factor in accelerating the spread of wildfire," says Baek Min-ho, a disaster prevention specialist at Kangwon National University.

Climate change is also to blame, experts say.

"This wildfire has once again exposed the harsh reality of a climate crisis unlike anything we've experienced before," South Korea's disaster chief Lee Han-kyung said on Thursday.

The ideal environment for these record blazes has been building for the past few weeks, which saw temperatures rise above 20C (68F), unusually high for spring. Analysis by Climate Central, which researches climate science, suggests that these high temperatures have been made up to five times more likely by global warming.

The unusual heat dried out the land and air, allowing fires to spread more rapidly, especially when combined with strong winds.

Dense tree cover and strong winds in the fire-hit region also pose substantial challenges to firefighting efforts.

On Wednesday, a 73-year-old pilot died when his firefighting helicopter crashed in Uiseong county. At least three other firefighters have been killed in the blazes.

Most of the 26 people who died are in their 60s and 70s, officials say. South Korea is an ageing society, where one in five people are at least 65 years old.

North Gyeongsang is its second-oldest province, which also explains the relatively high death toll - it is especially difficult to evacuate older people in a disaster because they may have mobility issues or other health risks.

They may also have more difficulty accessing or interpreting evacuation orders.

Three residents of an elderly care facility in Yeongdeok county died on Wednesday, when the car they were in went up in flames. Only one out of four in the vehicle managed to flee in time, the Korea JoongAng Daily reported.

Acting President Han Duck-soo said on Thursday it was "worrying" that many of the victims are elderly, as he ordered the interior minister to relocate to North Gyeongsang to oversee relief efforts.

An Andong resident who evacuated but lost her home told the BBC her family and their neighbours were caught off guard by the fires.

"No one in the village was prepared," said the woman, who asked not to be named.

"We had to leave with nothing, and all our belongings are gone. Many of the residents are elderly, so I hope the government can provide temporary shelters where people can stay comfortably," she said.

Historical relics have also been burned to the ground - a significant loss to an area considered one of South Korea's cultural centres.

These include treasures in two temples, each more than 1,000 years old. One of them, the Gounsa temple, dates back to the Silla dynasty (57BC to 935AD).

Additional reporting by Rachel Lee and Jake Kwon in Seoul