"[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.''
The local said a truck had smashed into the passenger side of a white Kea campervan.
While speaking to the survivors from the campervan - the dead woman's husband and daughter - she was told the man was driving and 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 father and daughter suffered minor injuries, a collection of cuts and bruises. The daughter had been in the back and was thrown around by the impact.
The truck's front was badly damaged, and the campervan was undriveable, the witness said. "It's a mangled heap.''
The intersection has recently been upgraded to improve visibility.
Patches of Waitomo Caves Rd leading to the highway were a rust-red colour. The large areas of coloured road surface coupled with numerous islands added to the road could be confusing, the witness said.
"I can understand how somebody who's not used to the country or roundabouts, mistaking that for a roundabout, not knowing that they're coming out onto 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 there had been two other crashes since the upgrade finished several months ago because drivers had been relying on old GPS navigational information.
"But this is the first time that I know of that [this] mistake has been made. But I do know it shouldn't be made again if anyone can help it.''
She has rung the New Zealand Transport Agency to push for signs warning drivers the intersection is not a roundabout.
"Everybody likes to place blame on somebody, but that doesn't help the situation if it happens again.''
The Waikato Serious Crash Unit was at the scene and Victim Support is expected to help the survivors after they're checked at Te Kuiti Hospital.