Triborough Bridge and Tunnel Officer Edward Grimm told the Staten Island Advance that the boy was turning colors and his eyes were going back and forth.
He said the belt was tightly wound around the boy's neck about eight times.
Grimm came upon the scene around 7 p.m. Wednesday when he responded to a disabled SUV on the span. When he realized what was happening, he called for assistance.
Grimm and Officer Lee Simons were able to free the boy by cutting the belt with Simons' folding knife.
The boy, Arthur Tyminsky, was taken to a hospital and later released.
Get Eyewitness News Delivered