A 14-year-old high school freshman died after collapsing during an Orange County cross country race.

Megan Nicole Myers of Dana Hills High School had completed two of the race's three miles Wednesday afternoon when she vomited, then attempted to run again and collapsed, authorities said. She was declared dead about two hours later at Mission Hospital in Mission Viejo.

Dana Hills was competing against Capistrano Valley High School in the meet at Laguna Niguel Regional Park.

The cause of death remained unknown. Preliminary results of a Thursday autopsy were inconclusive, and definitive results were not expected for up to six weeks.

"It's a mystery," said sheriff's spokesman Jim Amormino. "Sometimes, these tragic things happen."

Myers' coach, a former Anaheim firefighter, administered CPR before paramedics arrived.

Friends said Myers was an avid athlete who had played soccer and run most of her life.

"She was the greatest kid, very bright and full of life," said Terry Tutton, a friend of Myers and her family. "She had always been a runner and very athletic."

Myers' brother is a 15-year-old sophomore who plays baseball at Dana Hills High. She also had an 8-year-old sister.