The New York Post said the vehicle jumped the curb outside Manhattan's Rockefeller Center, hitting a 22-year-old British tourist, severing her left leg below the knee.
A pizza-truck owner grabbed the limb and put it in a bucket, then collected ice from street vendors to preserve it until medical personnel arrived.
He and other passers-by used a dog leash as a tourniquet to stop the bleeding on the left leg, while a plumber used his belt to try to staunch the bleeding from the woman's right leg, the Post said.
Oz told the newspaper he was at his nearby office when he heard the crash and ran down to the street to offer assistance. He told the newspaper everything appeared to be under control when he arrived.
"These guys saved her life," Oz told the Post of the Good Samaritans.
The woman was taken to Bellevue Hospital where her condition was not immediately known.
The Post did not say if the cab driver, who remained at the scene, was cited for the incident.