Three people died at the scene. Photo: Mike MacKinven
A fourth person has died after a crash near Lake Pukaki.
The crash between two vehicles and a motorcycle happened between Hayman Road and Tekapo Canal Road on Saturday.
Three people died at the scene, two of whom were foreign students from Malaysia.
Another three were airlifted to hospital in a serious condition and two people had moderate injuries.
Police said the fourth person to die was one of those in a serious condition.
They died from injuries overnight.
Police said the scene of the crash was harrowing and the were investigating it while also working on formally identifying those who died at the scene.
They spoke to several people present at the scene following the crash, but are asking for witnesses to come forward "in order to build a complete picture of what occurred".
Anyone with information is asked to contact police on 105 or report online, quoting file number 240331/4655.
The death takes the Easter weekend road toll to seven.
Two students from Malaysia died in the crash. Photo: X / Anwar Ibrahim
On Sunday, the Malaysian government confirmed five Malaysian students were involved in the crash.
"The ministry and High Commission of Malaysia stand ready to assist should the next-of-kin decide to repatriate the remains to Malaysia."
The University of Canterbury said it was "deeply saddened by the passing of two of our students at Pūkaki this weekend".
Vice-chancellor professor Cheryl de la Rey, in a statement, said two of the university's students were also injured in the crash.
They are in a stable condition in Christchurch Hospital.
"We will be working directly with Ōtautahi Christchurch's Malaysian community to ensure they have the support and help they need."
De la Rey encouraged students and staff to prioritise their wellbeing.
"Our thoughts are with those involved in the emergency service teams, and members of the public, who responded to the scene."
In a statement, the New Zealand International Students' Association said their hearts ached for those affected by the tragedy.
"This heartbreaking event has deeply impacted not only the families and friends of the victims but also the wider Malaysian student community in New Zealand," it said.
"We extend our sincerest condolences to the families and friends of the victims. We grieve with you during this difficult time."
'Seven Easters ruined and seven avoidable deaths'
Superintendent Steve Greally. Photo: RNZ / Alexander Robertson
The road toll this Easter weekend has been everything police do not want to see on the roads, they say.
"Up and down the country, road policing staff have seen drivers overtaking on congested roads, speeding and taking unnecessary risks," says Superintendent Steve Greally.
"Seven people have lost their lives and several others are seriously injured.
That's seven families that will never see their loved ones again, seven Easters ruined and seven avoidable deaths."
A further three people have died in crashes in Waikato, Bay of Plenty and Tasman.
"A crash where people are dead or seriously injured is a horrific scene, and I cannot but commend the staff that respond and serve with utmost professionalism," said Greally.
In Waikato, police were urging drivers to be mindful of agricultural vehicles, which often travel slower that other vehicles on open roads.
Three crashes involved tractors on Saturday and police were asking motorists to be patient and only pass when it was safe to do so.
Federated Farmers Dairy chair Richard McIntyre said a challenge for tractor drivers was pulling over safely for traffic to pass.
Sometimes build-ups could be caused because some drivers lacked the confidence to overtake a tractor, he said.
Police in Bay of Plenty, Southern and Canterbury districts also wanted their drivers to take it easy.
"Slow down - we can't say it any other way.
"Speed is a top contributor to serious injury and death in a crash, and with the Easter Weekend traffic and roadworks, speeding is the last thing anyone should be doing," said Greally.
Motorists should also be taking the conditions into account as they head home today, he said.
"In some areas the weather is beginning to turn.
"Sunny Nelson is having one of three bad weather days of the year and we ask anyone travelling in that area to drive to the conditions."