Ports of Auckland has stopped the use of its 27 automated machines after one of the robots jumped a concrete barrier, hitting a shipping container.
The automation part of its business has been halted while an investigation looks into how a robotic machine was able to jump a retaining wall, hitting a shipping container at the weekend.
WorkSafe has been advised and is looking into the incident.
The council-owned company is already under fire for major delays in clearing a huge backlog of cargo.
"It has a number of systems that control what it's meant to do. The system became overloaded, instead of turning left it went straight ahead," Ports of Auckland spokesperson Matt Ball told Checkpoint.
"That went over a low retaining wall… then it hit a container and came to a stop. The systems kicked in and stopped it then."
The straddle carrier weighs about 70 tonnes, Ball said.
"It was not dangerous to any people. The way we have the system set up, we operate… multiple layers of safety.
"There's one big external layer of safety, like the castle wall, and that is meant to keep these machines in there. That has been very robustly tested, through multiple system checks. That is a geofence, and what that will do is stop any of these machines from leaving their enclosure."
Ball said the geofence is tested to a higher degree than the system that runs the straddle carrier, and they operate on different systems.
"We would not allow it to run if we had any inkling that people outside of the enclosure would not be safe, it has been really, really rigorously tested.
"The system at the moment is still in the process of test and optimisation and improvement. So what's happened over the weekend is actually something that's sort of within the parameters of what we might expect. Ideally we don't want it to actually come into contact with anything, but we know that we are going to get little bugs and flaws in the software and that's part of the process that's underway at the moment."
All 27 automated straddle carriers are out of operation while the issue is investigated, he said.
"It hasn't actually had a major impact [on delays]," Ball said.
"It has slowed down the truck side of the operation a little bit. But we've been able to rejig our labour, and we've actually sped up the ship side of the operation."
Workers have been allocated to different cranes and concentrated on one ship at a time, he said.
Even though part of the operation has sped up with the reorganisation of workers, Ball said that is only a short-term fix, and Ports of Auckland is pushing on with the automation plan, as it is restricted in space at the waterfront.
He said the port has worked through a number of bugs with the automation system but it was not unexpected in comparison to automated systems overseas.
"We've notified [WorkSafe] of it, it's a standard practice… We'd absolutely notify whether it was a person driving or whether it's a robot."
The software has been updated and the port is testing now. Ball said they will make a decision on Tuesday morning on reactivating the automated system.
Earlier in November ships were reported to be waiting to enter Ports of Auckland for up to 12 to 14 days to unload. Ball said the wait time had reduced to an average of eight days.
He said the port had been able to hire a few more workers with the right skills, and was lucky to hire an experienced crane operator.
"And we've had a number of straddle drivers come back to work for us, who previously worked at Ports of Auckland. And we've got some good people in the pipeline. So some of them have been new, we'll have to train them, and we've got some people in training at the moment.
"But we are hoping we should be able to have a full crane crew in place by Christmas."