A passer-by desperately tried to save the girl but watched in horror as the train hit her.
The victim, who was in her late 20s, became trapped as she tried to cross a railway line after the crossing gates had shut.
One of the trendy ugg boots sale she was wearing got caught between the slats of the wooden guard at the level crossing at Hythe station in Colchester, Essex.
She was unable to move until passer-by, Jonathan Smith, intervened.
The IT student managed to help the woman free her foot seconds before the impact.
But he said that instead of getting out of the way of the train she tried to follow her boyfriend to the other side of the tracks.
Mr Smith, 18, said he went through the barriers and when he saw the woman had her foot stuck he grabbed her hand and she managed to free her foot.
"I had her in my arms. She was safe. But her boyfriend screamed at her to get to the other side," he said.
"I said 'Stay on this side’ but he told her 'This is my train, I’ve got to be on this side of the track’.
At this point, Mr Smith said the train was only about 25 feet away but the driver did not have a chance to stop.
"She just curled up in a ball and her boyfriend jumped out of the way," he said.
"I tried to help her but I slipped because it was wet. It was just luck that I wasn’t hit.
"I was still holding her hand when the train came but my friend told me to let go, otherwise I would lose my arm. I just went into shock afterwards.”
Despite Mr Smith's brave attempt to save the woman, identified locally as Kelly, she was killed instantly when a train travelling at between 40 and 50mph careered into her.
One of the men who had been trying to rescue the woman was treated in hospital for leg injuries following the appalling incident at 7.50pm on Thursday.
Today Detective Inspector Terry Pearce of British Transport Police paid tribute to the bravery of the two men who tried to save her.
He said: "This was a very valiant effort. They were very brave and we are very grateful not to be looking at two deaths or maybe even three.”
DI Pearce also paid tribute to the train driver who blared his horn in warning and stamped on the brakes in a vain attempt to avoid hitting the woman.
He said: "Certainly in this instant the driver actually saw something at the very last minute and tried his best.
"He applied the emergency brakes but because of the momentum of the train he was unable to stop in time.
"It was a harrowing experience for him and a harrowing experience for the witnesses and the police officers called to deal with this incident.”
The woman was hit by the 6.38pm National Express East Anglia train from London Liverpool Street to Clacton-on-Sea, Essex.
Locals said the crossing was dangerous and people often tried to slip through the barriers before trains arrived.
Matt Wilson, who was on the 6.38pm train, said: “It’s awful. I was in the first carriage last night.
"There was no warning, the driver just slammed on the brakes. Just a minute later you heard the sirens.
"We were stuck on the train for over an hour before we were released and had to climb up ladders."
The wooden guard lies next to level crossing to stop animals from veering onto the tracks.