A man in his 60s who was participating in a triathlon event held in Saemangeum -- reclaimed land in North Jeolla Province -- drowned to death during the swimming portion of the event, police said Sunday.

The 62-year-old man surnamed Kim was spotted floating in the sea by a lifeguard at 7:45 a.m. during the Challenge Gunsan Saemangeum International Triathlon competition.

He was pulled out of the water by an emergency rescue boat and taken immediately to a hospital where he received CPR before being declared dead.

Police believe the cause of death was a heart attack and are investigating the exact circumstances of the accident with event organizers.

Police said they would secure closed-circuit TV footage to investigate what happened and look into potential problems in the operation of the competition.

Having kicked off Friday, the triathlon competition saw the participation of more than 1,500 athletes over the weekend.

The event consisted of a swimming principle of 3.8 kilometers, a cycling portion of 180.2 kilometers and 42.2 kilometers of running around the Saemangeum seawall.