Mid South Canterbury police area commander Inspector Dave Gaskin said the minivan with six people was travelling on Cochranes Rd and appeared to have driven through a controlled intersection with Wakanui Rd and collided with a heavy truck.
Three people died at the scene, and one later in Ashburton Hospital, all occupants of the van.
The other two occupants of the van were also injured. One is in a critical condition in hospital and one in a serious condition
The truck driver, believed to be a local, was also hurt and is in Ashburton Hospital.
Those in the van appeared to be a group who had travelled from the North Island, Insp Gaskin said.
Police were trying to find out exactly what happened.
"This is an absolute tragedy and a terrible start to Queen’s Birthday. It appears a moment’s inattention has caused this tragedy. I urge people to be careful — take their time and be careful."
The crash was caused by a "moment's carelessness" and not connected to this week's flooding event.
"Any fatality is a hardship on the community. Ashburton and Mid Canterbury area has suffered a number of these types of accidents," Insp Gaskin said.
"All I can really stress is be very, very careful on the roads. It is up to all of us to do our bit."
The official holiday period began at 4pm yesterday and ends at 6am on Tuesday.
— The New Zealand Herald/ Linda Clarke, of Ashburton Courier
