A twin-cab utility vehicle carrying two adults in the front and three children in the back crashed into a bridge on Tuapeka Mouth Rd, 4km northwest of Clydevale, just before midnight on Saturday.
Police yesterday released the names of the two people killed in the crash.
They were Waitahuna farmer Anthony David Calder (45) and a family friend, 14-year-old Matthew David Beaumont, of Tuapeka Mouth.
An 11-year-old boy - believed to be Mr Calder's son - received serious injuries and underwent surgery at Dunedin Hospital and last night was reported to be in a serious but stable condition in the intensive care unit.
His injuries were considered life-threatening, Sen Const Robert Wallace said.
A 37-year-old woman - believed to be the wife of the dead man - and another 14-year-old boy, believed to be her son, received minor injuries.
The names of the three survivors have not yet been released by police.
Senior Constable Wallace said it was one of the most horrific crashes he has attended in more than 20 years policing.
"It was a real nasty one," he said.
Although police have said alcohol was involved, they are not commenting on which of the two adults was driving or what the group was doing in the hours leading up to the crash.
Speed was not thought to be involved but there was heavy fog at the time, Sen Const Wallace said.
"We can't say much more until we wrap up our investigations."
He would not comment on the possibility of any charges being laid.
The police serious crash unit from Invercargill conducted an initial scene examination early yesterday and another again yesterday afternoon.
More details may be released today.
The double tragedy has rocked the tight farming Clutha Valley community.
Both families involved are long-standing residents.
The seriously injured 11-year-old boy is a pupil at Clutha Valley Primary School, while the two 14-year-olds were best friends and former pupils at the school.
Both attended South Otago High School.
School board of trustees chairwoman Gaye Cowie released a brief statement:
"This is a sad time for our school community and our thoughts are with the families involved.
Our priority is to make sure our students are cared for and well looked after."
She confirmed counselling services had been arranged for when pupils return to school today.
Several hours after the Clutha Valley crash, a Wellington accident claimed the life of a 21-year-old man, NZPA reported.
The man was killed instantly when the car he was a passenger in crashed into a roadside fence in the Wellington suburb of Northland about 4am.
The three deaths on Saturday night brought the weekend road toll to four, after an 18-year-old woman was killed in a crash in Christchurch on Friday.
Talia Loren Burt died at the scene when the car in which she was a back-seat passenger crashed on Lower Styx Rd about 6.30pm.
