Smoke rises from a fire that broke out at Banyan Tree Haeundae Busan's construction site in the southeastern coastal city's Gijang County, Friday. Yonhap

A fire broke out at a resort complex construction site in the southeastern city of Busan on Friday, killing at least six people.

According to the Busan Metropolitan City Fire & Disaster Headquarters, the fire started at around 10:51 a.m. at the construction site for Banyan Tree Haeundae Busan in Gijang County of the city. Fire authorities began combating the flames using helicopters and other resources about 20 minutes after the fire started.

A helicopter is mobilized to rescue construction workers from the rooftop of Banyan Tree Haeundae Busan's construction site in Gijang County, Busan, Friday, as the building caught fire. Yonhap

Six people were found in a state of cardiac arrest at the scene, and all were pronounced dead later. Twenty-seven others suffered from minor injuries, while about 100 people evacuated from the scene, including 14 who escaped to the rooftop where they were rescued with helicopters.

The rescue authorities are continuing search operations to check for any remaining victims.

The fire is believed to have started from insulation materials stacked near the indoor swimming pool on the first floor of one of the three buildings under construction.

After about an hour, the regional fire authority upgraded the response level to mobilize personnel and equipment from more than 10 fire stations in the region. More than 120 fire trucks and 350 firefighters were sent to the scene. The police department also sent officers from its criminal, traffic and local police divisions to the scene to control traffic around the site.

Upon receiving the report of the fire, acting President Choi Sang-mok ordered acting Interior Minister Ko Ki-dong and National Fire Agency Commission Huh Seok-gon to ensure "thorough search and rescue efforts to prevent loss of life, while also securing the safety of firefighters."

Firefighters extinguish flames at the Banyan Tree Haeundae Busan construction site in Gijang County, Busan, Friday. Yonhap

Minister of Employment and Labor Kim Moon-soo also ordered the establishment of a response headquarters to investigate the incident thoroughly, including determining the cause and whether there were violations of the country's industrial safety law.

Banyan Tree Haeundae Busan is a five-star resort complex with three 12-story buildings, scheduled to open in the first half of this year.