The campervan appears to have made a full u-turn - the truck hit the left hand side of the vehicle. The NZL Group truck driver was shaken but unhurt.
A resident heard the truck screeching to a stop and rushed from her house.
"[I heard] a huge truck and trailer unit screeching its brakes to try and miss a poor tourist who mistook the intersection for a roundabout."
She was told the campervan driver thought the intersection was a roundabout.
"The truck driver would have never guessed that they were going to pull out. The guy in the van, he just thought he was on a roundabout.
"[The driver was] obviously distressed ... He was absolutely mystified as to what happened."
The Canadian tourists stayed at the Waitomo Top 10 Holiday Park on Wednesday but checked out after leaving Waitomo Adventures.
The resident said patches of Waitomo Caves Rd leading to the highway are a rust-red colour and this, coupled with numerous traffic islands, could be confusing for motorists.
"I can understand somebody - who's not used to the country or roundabouts - mistaking that for a roundabout, not knowing that they're coming out on to a main road.
"You haven't got a moment when a truck is coming from the south, at 100km/h ... It's just lethal there."
She said she had previously phoned the New Zealand Transport Agency to push for signs warning drivers that the intersection is not a roundabout.
Waitomo businessman Nick Andreef said it was a notorious corner, "and there's been that many crashes there".
"But recently there's been an upgrade on the corner," he said.
The improvements included better visibility and installing acceleration and deceleration lanes.