She was rushed to Lutheran Medical Center, where she was pronounced dead.
Officials say the green arrow at the intersection stays green all the time unless a pedestrian presses a button to change the signal. They say the woman would've been crossing with her back to the ambulance at the time.
"It is a dangerous crossing, because there's a lot of traffic," said Jeannie Lee.
The ambulance was carrying a patient with abdominal pain.
The victim was not carrying identification, but was crossing the street with a walker.
The FDNY and the NYPD are trying to determine if the ambulance was using lights and sirens at the time of the accident.