Hawaii island police are investigating a possible drowning Wednesday off Kona involving a diver who became unconscious during a dive tour.

The Hawaii Police Department responded to Honokohau Small Boat Harbor after receiving a report of the incident, which took place around 5:30 p.m. Wednesday.

Police said the dive tour boat departed around 4 p.m. and was 50 yards from shore when one of the guests on board, identified as 64-year-old San Diego resident Larry Bullock, became unresponsive.

Bullock was given cardiopulmonary resuscitation for 45-60 minutes as the boat made its way back to Honokohau. Medical personnel continued CPR, but Bullock remained unresponsive. He was transported to and pronounced dead at Kona Community Hospital.

His exact cause of death is still being investigated, police said.