The police are now saying that the person fatally struck by the train was a woman, not a girl. Inspector James Murtagh, a police official at the scene, said she was in her 40s. He did not offer further details.

A girl was crushed to death between a subway train and the platform at the 77th Street station of the No. 6 train on Thursday afternoon, officials said.

The police said that the girl had jumped to the tracks. Two eyewitnesses said that she had dropped her backpack and gone down to retrieve it.

Ninnie Hernandez, 13, a seventh-grader at Wagner Middle School on Manhattan’s Upper East Side, said that she was on the southbound platform when she said a teenage girl with blond hair and a blue sweater jump down from the platform on the northbound side.

“She dropped her backpack and she jumped in,” Ninnie said. A northbound train came charging into the station.

“People were telling her to lie down,” said Jahmal Reid, also 13, who said he was standing with Ninnie. “But she was too scared.”

The witnesses said the girl tried to pin her body flat against the platform wall, but she was crushed by the train as it pulled into the station.

The packed train came to a stop most of the way into the station. Part of the girl’s head and arm were visible between the platform and a door of a car toward the front of the train. Passengers inside the car were screaming.

The Fire Department confirmed that the girl had died.

Glenda Farr, 52, of Harlem, was in the second or third car.

“We felt a horrible thud,” she said, and then the lights went off in the train. “It was horrible. I’ve never felt anything like it, that terrible boom.” The lights started flickering and the train went dark momentarily. A motorman came over the loudspeaker and instructed passengers to walk to the front of the train to exit. Much of the train was still in the tunnel, she said.

Celeste Arthur, a traffic enforcement agent, was in the first car on her way home from work, when the motorman began beeping his horn. She heard three or four urgent, lengthy honks, before the crash.

“I heard this blowing and then the impact. You felt it,” she said. She described a slightly panicked but orderly exit from the train, which had been fairly crowded. The platform was full of schoolchildren, she said.

Neelema Singh, 17, a college student from the Bronx, described a chaotic scene as she exited the train.

“A lot of kids were running and crying,” she said.

The train was moved out of the station at 5 p.m.

Anne Barnard, Michael S. Schmidt and Liz Robbins contributed reporting.