Hargest said the crash appeared to be a head-on between two cars, one carrying the dead and injured, and another towing a trailer.
Two people in the car towing the trailer were uninjured and checked at the scene.
The female driver and male passenger were towing furniture, Hargest said, and were moving house from Wallacetown to Timaru.
The woman told Hargest she had no time to react before the impact.
He said it was unclear what caused the accident but it happened on a sweeping bend where there had been other less serious crashes over the years.
The 100kmh road took high volumes of stock trucks, milk tankers and commuters, Hargest said.
"It's a very busy road. There is a lot of traffic on it and it's quite windy today so whether that played part of it I don't know.
"It's a bit of a sad Christmas for quite a few people I would imagine."
Hargest said his wife called him from Arrowtown to check he was okay after his nephew in Auckland spotted the story on the Herald online and rang his mother in Twizel to make sure Hargest was not involved in the crash.
The eastbound lane was still blocked and diversions were in place.
Police said motorists should expect delays while the Serious Crash Unit investigate.