A 36-year-old man free diving off Kaimana Beach in Waikiki ran into trouble and was taken to the hospital where he died.
Emergency Medical Services said the man was free diving with a friend at 5 a.m. Friday in front of Kaimana Beach.
When firefighters arrived, police officers were applying CPR.
Paramedics took over and transported the victim to the hospital in critical condition.
Police have classified the apparent drowning as an unattended death.