According to the international triathlon federation, World Triathlon, the death occurred after a traffic accident during a training camp in France.
Miyazaki was reportedly riding a bicycle when she was hit by a car. She was in France to prepare for the 2024 Paris Olympics.
The 25-year-old competed in the WC in Spain’s Pontevedra last week.
In a statement, World Triathlon and the Japan Triathlon Federation send “their deepest condolences” to Miyazaki’s family and friends.