The overturned truck was on the railway side of the road.
The witness, who would not be named, said he was travelling from Whakatāne to Tauranga when he came across the scene, he believed just minutes after the incident happened.
He said he saw that a person was being helped from the cab of the truck and first responders were arriving at the scene.
Video from the crash scene shows a truck and trailer on its side half on the road and in the paddock.
Contents from the trailer had spilled on to the side of the road.
Diversions in place
An initial traffic alert from NZTA said: “Due to a crash east of Rodgers Rd, lanes are blocked.
“Expect delays and pass the scene with care.”
Diversions are as follows: Eastbound traffic should travel via Pukehina Station Rd and Old Coach Rd and rejoin SH2. Westbound traffic should do the reverse. Heavy vehicles should use SH33 and SH30.
A 3.15pm update said the section of SH2 was “likely to remain closed for some time today as NZ Police undertake a serious crash investigation”.
A witness at the scene earlier told SunLive a helicopter had arrived and police were working on diversions.
”It’s a quick diversion but we are at the start of the line, so it might get worse soon.”
A St John spokeswoman said they were celled to the incident at 1.49pm and responded with one ambulance, multiple other vehicles and a helicopter.
As at about 3.45pm the ambulance was still at the scene.
A Fire and Emergency spokesperson said two fire appliances attended.
More to come.