The fatal incident happened shortly after 6 p.m. at the Sylmar/San Fernando station in the 12200 block of Frank Modugno Drive, according to the Los Angeles Fire Department.
"I was just on my phone and somehow I felt like a bump," said train passenger Edder Vargas, describing the impact. "And I was like wondering: Did we hit something?"
The woman was pronounced dead at the scene. She was not immediately identified.
A witness said that the woman and her friends were pretending to dodge the oncoming train just before the collision.
#UPDATE: Police say victim who fell on metrolink tracks is 24-years-old. A witness who was on the platform says victim was messing around with her friends and pretending to lean into oncoming train when she slipped. Police say boyfriend & friends tried to help but it was too late pic.twitter.com/xka8o4ROJz— Veronica Miracle (@ABC7Veronica) April 17, 2018
"When she was leaning back and forth -- kind of like, as if you play tug-of-war, how you lean -- she was doing that and ended up losing her footing and slipped," said the witness, a woman who declined to be publicly identified.
After the victim fell between the platform and the train, her boyfriend and friends tried to help her.
"Him and another male grabbed her hand, trying to pull her out -- and that's when it hit her," said the witness, one of several people who saw the tragedy unfold. "It was an accident -- she didn't mean to die. She was scared and it's really sad."
The Metrolink Antelope Valley Line 285 train, bound for Palmdale, was stopped at the station after it hit the woman. Line 221 to Lancaster was held at Sun Valley due to the incident.