It also advised motorists they may want to consider washing their vehicle to get rid of the unintended paintwork if they drove through before cordons were put in place.
The agency said there were now two lanes open for traffic to use with one lane before the exit to the Mt Wellington Highway still closed.
For the past two hours there has been just one lane open for traffic to use on a section of Auckland's busiest highway.
Cameras showed vehicles down to a snail's pace from Newmarket as they filed into the single lane left open to pass by the clean-up operation.
Just before 12.40pm NZTA said the mop up was finished with delays from Greenlane to Penrose starting to ease.
Meanwhile, drivers using SH29 over the Kaimai Range in the Bay of Plenty were urged to take extra care and slow down due to an oil spill on the road which had led to a spate of crashes.
The highway is down to one lane each way while contractors cleaned up the oil that had created a 300m slick.
The spill happened after a ute and car crashed just around 10.10am near the summit on the Matamata side of the range.
The slippery surface has led to three minor crashes on the highway.