A truck has run off the motorway at Papakura, north off the Karaka on-ramp.
NZTA Auckland and Northland tweeted there had been a crash on the Southern Motorway north-bound after the Papakura off-ramp.
The left lane was blocked and traffic was warned to expect delays.
A Fire Service spokesman said it was a "truck versus tree" situation.
A truck had crashed into the motorway barrier and into a tree.
No one was trapped.
A Twitter update from NZTA said: "The earlier crash on the Sthn Mwy N-bnd after the Papakura off-ramp has created traffic delays back to the Drury off-ramp."
An NZTA spokeswoman said traffic was moving very slowly.
"We encourage people to allow extra time or avoid the area if possible."