At least six people were killed and 25 injured in a fire at a construction site for a luxury hotel in South Korea.

The inferno reportedly broke out at the pool area on the ground floor of the Banyan Tree hotel in port city Busan at around 10:50 am today, February 14.

Firefighters arrived at the scene as thick black smoke billowed from the 12-storey building.

Six construction workers were found 'in a state of cardiac arrest' at the pool area blanketed in choking fumes from burning insulation material. Twenty-five others were found throughout the building with minor injuries from smoke inhalation.

Helicopters were deployed to rescue 14 people who had fled to the rooftop.

The National Fire Agency said 124 firetrucks, 352 firefighters, and three fire helicopters had been dispatched to extinguish the fire and conduct search operations.

Authorities said the blaze was under control by 1:30 pm.

Hong Moon-sik, chief of the Gijang County fire department, said: 'The cause of the high number of casualties was that the fire had already spread by the time we arrived on the scene.'

The cause of the fire was under investigation, officials said.