New images of damage to the Auckland Harbour Bridge show bolts shorn clean off by the impact of a truck crash.
Engineers found "significant" damage to the bridge in an overnight assessment and predict that it will take weeks to repair, during which time some lanes will have to be closed.
All four centre lanes of the eight-lane bridge were shut today, causing congestion in both directions.
Images released by the Waka Kotahi NZ Transport Agency show the extent of the damage to a load-bearing strut on the bridge's arch.
"The upright strut is fixed to the bridge top and bottom with a series of bolts," said Waka Kotahi Senior Journey Manager Neil Walker.
"These bolts have sheared off and left the strut detached at the bottom. The strut is bent and twisted at the point it was hit."
The bridge was damaged yesterday when two trucks crashed in quick succession after being tipped by wind gusts of up to 127km/h.
The damaged strut helped support the bridge's weight, Walker said.
"Bridge engineers are assessing how to repair or replace the strut, while also checking if other struts were damaged, given they've had additional load transferred to them. The sheared end of the damaged strut has been temporarily bolted back on to the bridge."
It was an important component of the bridge's structure, but there was no risk to the bridge's structural integrity or overall safety.
However, there are likely to be lane closures for weeks while it is repaired.
The agency urged motorists to adjust their travel plans and usual patterns if they wanted to avoid the disruption caused by the lane closures.
They were advised to use the Western Ring Route via SH16, SH18 and SH20 instead. "While the Western Ring Route was carefully planned and constructed to be used as an alternative to the Harbour Bridge, especially for trucks and heavy vehicles, it will now also experience congestion and delays with the additional traffic volumes that would have been on the Harbour Bridge," Walker said.
Motorists were also asked to consider working from home where possible from Monday. If they had to travel, they should consider using public transport.
The Northern Busway would be operating and buses could safely use the "clip-on" outside lanes.
Two trucks crashed around 11am yesterday in high winds. A NZ Van Lines truck carrying an empty shipping container, was blown sideways on the outside, southbound lane and hit the bridge superstructure. No one was injured in the crash, though the driver's boss said he was "in shock" at the time.
Immediately before that, a Castle Parcels truck driving northbound was blown across two lanes and toppled over the moveable lane barrier, becoming stuck. The driver was taken to hospital but was not badly hurt.
Lane closures caused by that crash led to gridlock across Auckland for more than six hours.
Around 170,000 vehicles cross the eight-lane bridge a day.