Drysdale, 34, called 111, and Taupo's Greenlea Rescue Helicopter was alerted.
"We stayed with him until the rescue chopper came and rescued him."
He said the injured man was in quite a lot of pain: "He was pretty shaken up when we first got to him, he was in shock and, although he had superficial cuts to his arms, he clearly had a very sore back.
"He wasn't able to get down the mountain himself.
"It was pretty clear what happened. Basically he was just coming down and lost control, tumbled forward, and grazed his arms on the rocks as he landed. He was trying to protect his face.
"Apparently he sort of rolled and kept tumbling for a little while - that was his main issue."
Greenlea Rescue Helicopter pilot Nat Every said the tourist was taken from the mountain on a long line recovery system "with back injuries and significant grazing to much of his body".
Meanwhile, the rescue helicopter returned to Tongariro Crossing yesterday for a 14-year-old boy who slipped while coming down from the red crater.
The boy, who was part of a school outing, slipped on a rock, injuring his ankle, and was unable to walk.
He was taken to Rotorua Hospital with a suspected fractured ankle.