An employee at the privately owned impact site called the sheriff's office about 4 p.m. Thursday to report a man trespassing at the bottom of the crater.
He then told authorities that he watched through binoculars as the man jumped feet first into the mine shaft, which is surrounded by a 7-foot-high fence topped with barbed wire.
It took hours for rescuers to get to the opening of the mine shaft, and they were battling 20-degree temperatures with a wind chill factor below zero.
They called out to Singh about 8:20 p.m. and got a faint reply, indicating he was still alive.
Sheriff's officials said rescuers lowered food, water, warm clothing, a flashlight and a portable radio to Singh so they could communicate with him.
A member of the Flagstaff Fire Department's technical rescue team was lowered into the shaft to provide initial treatment to Singh, who they said had severe hypothermia.
Singh was carried up the 600-foot crater incline and then more than a mile to the visitor center's parking lot before he was transported to a hospital.
More than 30 responders from various agencies around Arizona assisted in the rescue, Blair said.