KEY POINTS:
An invisible, decades-old septic tank caused the collapse of a 41-tonne crane in Tauranga yesterday.
No one was injured, but a building site was damaged and a hook at the end of the crane narrowly missed hitting traffic on one of the city's main roads.
A section of Cameron Rd, Greerton, was closed during morning rush-hour as the crane company worked to resurrect the fallen boom.
About 40 people watched the salvage effort.
The base of the Kato crane was up-ended when it fell into the septic tank, leaving the wheels exposed.
Crane company Titan had not known about the tank, which lay hidden beneath asphalt next to the building site.
Regional manager Russell Richardson said the tank was not on any plans of the area and was probably about 70 years old.
He said such situations were a nightmare for crane operators.
"It's an occupational hazard," he said. "You can't see what's under the ground."
The crane was lifting steel roof trusses on to the building site when the incident happened about 7.15am.
"It's gone straight through the septic tank and it's become unstable and collapsed," Mr Richardson said.
The crane's boom hit the top of a three-storey building being constructed on the site, damaging an outside wall and destroying scaffolding.
The boom also suffered extensive damage.
Mr Richardson said several motorists had stopped in surprise when they saw the crane's hook hit Cameron Rd, but the road was relatively quiet at the time and no vehicles were hit.
The crane had a 50-tonne lifting capacity and larger cranes were needed to lift the damaged boom off the building.
The two other cranes, one with an 80-tonne capacity and the other with a 60-tonne capacity, righted the boom but it would not retract and faced being cut off.
Despite the damage, Mr Richardson was thankful the collapse did not result in injury.
"You buy insurance for this sort of thing. No one's hurt and that's absolutely critical."
The crane driver was said to have had a major fright.