Taumarunui Fire Station chief Barry Fisher said there were "bodies everywhere'' when they arrived at the isolated scene.
"It was out in the country and not much radio contact.''
A nearby farmer had notified authorities and used a crowbar to free one person who was trapped before emergency services arrived.
Mr Fisher said one of the vans appeared to have driven onto the wrong side of the road. The shearing van had been carrying a trailer which had jack-knifed.
Senior Sergeant Grant Alabaster said there were eight tourists in one van and 10 local workers in the other.
Preliminary findings showed one van had been on the wrong side of the road going around a corner.
Alcohol was not thought to have been a factor.
Taupo Greenlea Rescue Helicopter also attended.