Otago Peninsula community board member Chris Garey lives next door to the affected property and saw the slip come down.
"If anyone had been under the slip I think someone would have been killed.
"The whole lot just cut loose. This huge part ... just dumped on the road, just like that. The noise was phenomenal."
Ms Garey first saw a small slip as she went past with her daughter.
It was raining "very hard" and she was concerned other drivers might not see it as they rounded the corner.
She went and got traffic cones but as more material fell, Dunedin-bound traffic began to back up.
"There is a lady out there who should go and buy a lotto ticket. She was very determined, she wanted to go to town.
"As she started to pull out to pass the first car, the headland just cut loose at that point. She would have been under it.
"It's an absolute miracle no-one was hurt."
The slip took with it three large trees and a shed belonging to Peter Raffills, who believes the slip occurred after a clay bank between two rocky outcrops became saturated by heavy rain.
The shed contained building equipment and scaffolding, he saidBoth Mr Raffills and Ms Garey said they were impressed by how Fulton Hogan and the Dunedin City Council had tackled the slip.
Ms Garey was less impressed by some impatient motorists who disrupted work by not observing the road closed signs.
She had seen cyclists carrying their bicycles around the slip to avoid taking the detour.
Contractors expected to have at least one lane of Portobello Rd open by last night.
Council roading maintenance engineer Peter Standring last night said initial estimates were that 500cu m of material would need to be cleared, but that had increased to more than 1000cu m.
