The truck was believed to be heading north.
Fire and Emergency New Zealand (Fenz) shift manager Alex Norris earlier said crews from Weston, Ōamaru and Waitaki responded to the crash.
Norris said crews used specialised equipment to free the occupants of a vehicle.
“Crews will likely be on scene for some time, so there will be delays,” he told the Herald.
Hato Hone St John said it was notified at 8.58am and sent two ambulances, two helicopters, and a manager to the scene.
NZ Transport Agency Waka Kotahi said due to the serious crash, the road was closed between Alma and Fortification Rds.
“Road users are advised to expect delays and to avoid the area if possible.”
Yesterday afternoon a person died after a single-vehicle crash on Ōtira Highway, Jacksons, in Westland.
Police said a further three occupants suffered minor injuries.
“An investigation into the cause of the crash is under way.”