A 50-year-old man in a following truck tried to take evasive action but couldn't avoid hitting the van. Lee said the man's manoeuvre may have prevented critical injuries.
The driver of the van called emergency services and was trapped in the vehicle until they arrived.
St John later said it sent two ambulances and four people were taken to hospital. One person was in a serious condition, two were moderate and one person had suffered minor injuries.
Waka Kotahi says the highway is closed between Henley Berwick Rd and the State Highway 86 intersection.
Detours are in place.
Another crash took place in the same road at 11.50pm on Monday. Lee said a 25-year-old man hit a patch of ice on the bridge and struck the barrier, which sent him into a spin.
The front of the vehicle was damaged and the left lane was blocked for about two hours before a tow truck removed it.
The bridge barrier was damaged in the crash, but there were no reported injuries.
Three injured in crash on Kilmog
Three people are believed to be injured after the car they were travelling in slid on ice, hit a parked truck and went down a bank on the Kilmog, north of Dunedin, this morning.
A police spokeswoman said the incident happened about 9.20am on State Highway 1, near Church Rd.
Police and St John are in attendance, and an Otago Regional Rescue Helicopter has been sent to the scene.
The people were trapped in the vehicle. Their injuries appeared to be minor.
A police spokeswoman said there were more than 30 crashes in and around Dunedin overnight, ranging from cars sliding down hills into lamp posts through to more serious crashes.
