Two victims of the fatal crash on Auckland's State Highway 1 were young men in New Zealand as seasonal workers, Samoan media report.
Three people died in a crash and three more people are hospital, one with critical injuries.
Samoa Global News said two of the deceased had been identified by their families in Samoa and were due to return home in two days time.
Another passenger, also a seasonal worker, was among the injured. Lying in a hospital bed he was seen on a Facebook live in tears, describing the accident to his colleagues, the report said.
The stretch of SH1 where the crash happened has reopened. Lanes were closed between Bombay and Ramarama following the collision of a truck and three other vehicles shortly before 2pm on Monday.
Tamati Cassin, a motorist who arrived at the scene about 30 seconds after the crash, said he saw three bodies in a van as well as three other people with injuries.
As he approached the scene in his car, Cassin said he saw a "big dust cloud" across the motorway and the wire from a metal barrier was strewn across the lanes.
Southern motorway reopens after fatal crash
"I had to pull over and I got out of my car - I wish I didn't now, I wish I didn't see the bodies.
"There were several cars involved but the van was the worst and even the truck was pretty smashed up on the cab it's a tragic, tragic accident."
Cassin said everyone got out of their cars to try and help the injured and dead but it was "chaos" and no one was sure what to do.
"I just really feel for the driver of the truck and the people who have passed, I get to go home to my partner and kid but they won't get to."
Counties Manukau road policing manager Inspector Tony Wakelin confirmed all three people who died were travelling in the same vehicle.
A huge number of emergency service staff attended the crash scene. Photo: SUPPLIED
"This many fatalities at once is shocking and our thoughts go out to all those affected.
"Incidents like this are hard on everyone involved and we are making sure there is support in place for those involved, their families, and our staff who have attended the scene," he said on Monday.
Anyone who witnessed the crash is asked to contact police, especially if they have dashcam footage.
Overnight, road crews put in a temporary steel barrier on the median strip, replacing the damaged wire rope barrier.
Waka Kotahi Auckland systems manager Paul Geck told Morning Report the barrier destroyed in the crash was an older type.
"There are different types of barriers. The newer ones are definitely better at stopping trucks and vehicles and this one was more of an older type."
Geck said he had no concerns about the integrity of the wire rope barrier.