At least 18 people have died as multiple wildfires rage across South Korea’s southeastern region, with thousands of firefighters aided by the military deployed in a bid to contain one of the country’s worst forest fires in decades.

The deadly wildfires have spread rapidly and forced more than 27,000 residents to flee their homes, the government said. The blazes, fuelled by strong winds and dry weather, have razed entire neighbourhoods, closed schools and forced authorities to transfer hundreds of inmates from prisons.

“We are deploying all available personnel and equipment in response to the worst wildfires ever but the situation is not good,” Acting President Han Duck-soo said, adding that the US military in Korea was also assisting.

As of Wednesday at 5 a.m. (2100 GMT), 14 people had died in a wildfire starting in Uiseong county, while four other deaths were linked to another fire in Sancheong county, according to the Safety Ministry.

Many of those who had perished were aged in their 60s and 70s, said Son Chang-ho, a local police official.

The Uiseong fire, only 68% contained and exacerbated by gusty winds, shows “unimaginable” scale and speed, said Lee Byung-doo, a forest disaster expert at the National Institute of Forest Science.

Dry conditions were expected to persist in the wildfire-hit region on Wednesday, the Safety Ministry said.

Climate change is projected to make wildfires more frequent globally, Lee said, citing the unusual timing of wildfires that ravaged part of Los Angeles in January and a recent wildfire in northeast Japan.

“We have to admit large-scale wildfires are going to increase and for that we need more resources and trained manpower,” he told Reuters.

South Korea relies on helicopters to help extinguish wildfires due to its mountainous terrain, but Lee said there was a need to bring in other fire-fighting aircraft and drones that can operate at night.

The Korea Forest Service said that it had grounded all of its fire-fighting helicopters after a chopper crashed on Wednesday while trying to put out a blaze. The pilot died in the crash, Yonhap News Agency reported.

Video footage from the scene showed what appeared to be a twisted fuselage alongside smoking debris scattered over a hillside. The cause of the accident was being investigated, authorities said.

The agency has been facing technical issues with its fleet of 48 Russian helicopters. Eight had been out of operation since last year due to an inability to import parts from Russia because of sanctions related to the Ukraine war, Yoon Joon-byeong, a Democratic Party lawmaker said in October, using data from the forest service.

Kim Jong-gun, a spokesperson for the Korea Forest Service, said the agency planned to secure more wildfire-fighting helicopters, responding to criticism about a lack of equipment and helicopters on the ground.

He said that 4,919 firefighting personnel were being deployed on Wednesday, including hundreds of police officers and military units, while 87 helicopters were being used.

The blazes that broke out on Saturday in Uiseong are yet to be contained, gutting ancient temples and destroying homes.

The Uiseong fires were also threatening several UNESCO World Heritage sites - Hahoe Village and the Byeongsan Confucian Academy - in Andong city on Wednesday, a city official said, as authorities sprayed fire retardants to try to protect them.

The flames had already burnt down Goun Temple, an ancient temple built in 681, Yonhap reported.

The government has designated the affected areas as special disaster zones, and said the fires had damaged more than 15,000 hectares (37,065 acres).