A newborn baby died Wednesday morning after becoming unconscious on a Green Line train -- despite a Metro worker's efforts to save him.

The baby was traveling with his mother and another boy who appeared to be less than 4 years old, said Tashiea Hodge, who was riding the rush hour train when it happened.

She heard the mother crying and screaming that she had just had the baby on Saturday.

An announcement was made, between the Waterfront and L'Enfant Plaza stations, asking for any medics aboard the train to quickly go to the second rail car, Hodge said. A woman wearing a Metro uniform came and started administering CPR to the infant.

"When we arrived to L'Enfant Plaza she went out onto the platform and was still giving the baby breaths and chest compressions," Hodge said. "Her training was evident and the fact she never stopped is to be commended."

The baby took a gasp of air and was faintly breathing, Hodge said.

Medics, who were called to the station about 8:15 a.m., then took over, said D.C. Fire and EMS spokesman Battalion Chief Brian Lee.

The baby was later pronounced dead at Children's National Medical Center.

Lee said there were no obvious signs of trauma, and he said preliminary information indicated the death was due to natural causes. But D.C. police are investigating while awaiting autopsy results, police spokeswoman Officer Tisha Gant said.

Metro declined to comment on the name of the worker who gave the CPR or her job at the agency.

After the medics took over, the Metro worker sat still for a minute and cried, Hodge said. She then went up the escalator, where she fainted. Two others helped her. She got up, took off her jacket and they all walked away.