A 24-year-old woman experienced a medical episode while running the New York City Marathon on Sunday afternoon.

Rachel Apa was taken to Mount Sinai Hospital in critical condition, where she died hours later, NBC News reported. 

Doctors told the family that she had died of rhabdomyolysis, a serious and rare condition that causes muscles to break down due to overexertion, trauma, medications or an underlying health condition, according to the Cleveland Clinic. 

The breakdown of muscles can lead to muscle death, and toxic components of muscle fibers enter the blood circulation and kidneys, causing kidney damage. 

Her father, Steve Apa, confirmed her death. He told NBC that he exchanged messages with Rachel Apa as she ran, and she said that she felt "amazing" and "never felt this good." 

He followed his daughter's progress on an app. After the mile 18 marker, Steve Apa said, his daughter began texting messages suggesting she was in pain. At the mile 24 marker, she stopped moving. 

New York Road Runners, which organizes the marathon, said in a statement that a bystander had administered CPR, and medical staff used a defibrillator on her, before she was taken to the hospital.