A truck has rolled and is blocking a motorway on-ramp in south Auckland, police say.

Emergency services were called to the Manurewa-Takanini on-ramp about 5.30pm.

Police said the motorway heading north was down to one lane. "Traffic is backing up and motorists should expect delays," police said in a statement.

The truck and trailer had rolled, blocking traffic onto State Highway 1.

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The driver was out of the vehicle and was not thought to be injured, a police spokeswoman said.

The Southern Motorway, looking south from Walter Strevens Drive. Photo / NZTA
The Southern Motorway, looking south from Walter Strevens Drive. Photo / NZTA

Contractors had been called to clear the on-ramp, which was strewn with debris.

Police asked motorists to use alternative routes. Diversions were also in place.