The officers found the baby girl and her mother inside the train station's bathroom.
Officer Bryan Richards gave the baby CPR, but she was still unresponsive and they rushed her to the hospital.
As Officer Alberto Nunes drove, the baby responded to chest compressions and started breathing.
The baby remains hospitalized at University Hospital, where she's expected to be okay.
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"It's obviously not something you see every day, but as a department it's something we do train on," said Richards, who told reporters he has a 7-month-old infant at home. "We do train in CPR training every couple of years to keep our training up.... When the stress and everything else... you do go back to your training. And that's exactly what we did."
WATCH: Hero NJT officers talk about saving infant
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