Delays are expected on Auckland's Southern Motorway following a gravel spill that left multiple lanes blocked near the Takanini off-ramp.

The spill has now been cleared and all lanes are open, however Waka Kotahi NZ Transport Agency warned motorists could expect delays until congestion had cleared.

The transport agency first tweeted about the spill around 1.15pm, saying it had affected lanes on State Highway 1 after the Takanini off-ramp, slowing traffic in the area.

At one point, Waka Kotahi said there was a 20-minute delay on the highway between Papakura and Takanini.