Three runners were fatally struck by a drunken driver during an ultramarathon race Thursday morning.

According to the police and the Korea Ultra Marathon Federation, the event’s organizer, the accident occurred at 3:30 a.m. in Icheon, Gyeonggi Province, four days into the 537-kilometer race which began in the southernmost point of Busan at 6 a.m. Sunday.

The deceased were running on the side of a two-lane road, with flashing guide rods on their back, when a Hyundai Motor Sonata sedan crashed into them from behind. The three runners were pronounced dead while being taken to the nearest hospital.

The police found the 30-year-old driver was under the influence of alcohol, with a blood alcohol concentration surpassing 0.08 percent, enough to revoke the driver’s license. The driver testified to the police that he did not see the runners while driving.

The event’s organizer, the Korea Ultra Marathon Federation, terminated the race following the accident.

The biannual race, whose course runs from Busan all the way to Imjingak in Paju, northern Gyeonggi Province, had about 75 participants this year. It is said staff from the race management team were present at a nearby check point, which was just about 500 meters from the site of the accident.

Runners were expected to arrive at the finish line by no later than 1 p.m. Friday.

“We tried to run the event with safety as our top priority, and we deeply feel the responsibility of not being able to avoid the fatal accident,” the Korea Ultra Marathon Federation said in a statement Thursday morning, offering condolences to the bereaved family members.

The police said they are investigating further details of the accident as well as whether due safety measures were in place to protect runners.

By Ko Jun-tae (ko.juntae@heraldcorp.com)