The incident happened at around 2 a.m. Saturday on Baychester Avenue in the Edenwald section of the Bronx.
The unidentified victim told the EMS crew he was suffering leg pains.
Authorities say after being taken to Jacobi Medical Center, he was pronounced dead.
Questions are being raised as to whether he was the victim of a hit-and-run.
Detectives are canvassing the area where the man flagged down the ambulance for surveillance video and other clues.
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