Police were alerted to the crash between Roxburgh and Millers Flat about 11.15am yesterday.
"Sadly, one person was located deceased at the scene," police said in a statement.
No other injuries were reported.
A motorist driving from Queenstown to Dunedin at the time said it was "just chaos" on the road.
"There was a convoy of motorhomes and they just weren’t pulling over, they were just speeding up, slowing down and people were overtaking them — it was just ridiculous.
"Where that crash was, it was a straight where there isn’t a passing lane."
Eventually, he felt so unsafe on the road that he pulled over at a petrol station to put some distance between himself and the convoy.
"I just had that gut feeling as soon as I pulled out."
He said he had barely gone down the road before two police cars were behind him.
"I pulled over, and then another one came by, and then an ambulance ..."
The highway was closed for some time while the Serious Crash Unit conducted a scene examination.
A witness said the crash appeared to have happened outside Transworld Roxburgh depot.
Motorists were advised to follow diversions and expect delays.
Transworld Roxburgh director Geoff Smith said the accident did not involve Transworld Roxburgh vehicles or employees.
"It was only coincidence that it was outside the gate to the entrance to our property."
Transworld provided assistance to victims until first responders arrived, he said.
— Additional reporting Ella Jenkins
