The top of Williamson Ave and the intersection with Ponsonby Rd were the worst affected areas.
Traffic was becoming congested as Auckland Council staff worked to clean up the spill.
They were expected to be there for much of the day.
Motorists were advised to take care.
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Meanwhile, a large amount of diesel also spilled on the Kaimai Range in Bay of Plenty this morning.
Police said the spill on State Highway 29 began near Soldiers Rd on the Tauranga side and extended over the ranges and down towards Matamata.
The surface was extremely slippery and several vehicles had already slid off the road as a result.
Motorists were urged to slow down and take extreme care.