Runner Rachel Apa, 24, collapses two miles from the NYC Marathon finish and dies after six hours of efforts to save her

Rachel Apa, a 24-year-old runner, has died while running the New York City Marathon. She collapsed at mile 24 of Sunday's race — just two miles from the finish line.

On November 1, Apa set out to run the world-famous race for the first time, along with more than 60,000 other runners. The former Bucknell University Division I field hockey player had trained for the marathon for months. On Monday, The New York Times reported details from her parents, Michelle and Steve Apa.

Her father, Steve Apa, was back home in Lewisberry, Pennsylvania, sending his daughter supportive texts at every mile as he tracked her in the New York Road Runners app.

Rachel texted her father back at mile 18, saying, 'Ow.' And once again at mile 19, 'Ow ow.' At mile 23, Steve texted, 'Final stretch.' Rachel never responded again, according to The New York Times.

Her mother, Michelle Apa, watched her daughter run by at mile 14 in Long Island City, Queens. She took a video of Apa looking strong, smiling and giving out high-fives before taking off again. Michelle then headed toward the finish line, planning to wait for her daughter at mile 25 in Central Park.

Spectator Michaela Nicholas saw Apa pass by near mile 24 in Central Park, in her matching green shorts and tank top, and cheered her on with only two miles to go. Seconds later, at around 1:30 p.m., Apa collapsed.

Nicholas, who is a hospital social worker, ran over to help and found that Apa did not have a pulse. After Nicholas's fiancée called for a doctor, two people who said they were physicians took turns administering CPR. Nicholas said she held Apa's hand the whole time.

The New York Road Runners, the marathon organisers, told the Times that marathon medical staff arrived soon after and used a defibrillator to try to revive Apa. Paramedics then arrived with an ambulance.

After realising Apa was no longer moving in the tracking app, Michelle Apa headed to her daughter's location; when she arrived, the ambulance carrying her daughter was pulling away. Rachel was taken to Mount Sinai Medical Center, where doctors worked to save her life for more than six hours. She was declared dead at around 9:40 p.m.

Steve Apa told The New York Times that his daughter's cause of death was rhabdomyolysis, a rare muscle condition that occurs after injury, severe dehydration and overheating, or, most typically, excessive, high-intensity exercise without rest. In this condition, over-exerted muscles break down, and toxic components of the muscle fibres can enter the circulatory system and kidneys, causing kidney damage and essentially acting as poison to the body.

'It's unfathomable,' Steve Apa said. 'Perfect health, perfect shape, 24 years old.'

Common signs of the condition include weak muscles, muscle stiffness and swelling, muscle pain and a change in urine colour towards brown, red or a tea shade. It can also lead to nausea, dehydration and loss of consciousness. Physicians recommend staying hydrated and avoiding overheating to avoid the condition.