The centre lane of Auckland's Northern Motorway heading northbound near the Upper Harbour Highway is blocking and causing major delays.

Congestion is swelling in the area following an incident after the Upper Harbour Highway off-ramp.

NZ Transport Agency reports the incident took place around 4.20pm.

Motorists heading home on the Northern Motorway are asked to pass the incident with care and expect delays.

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A crash is also blocking a lane on the Southern Motorway at the Greenlane off-ramp.

Meanwhile, motorists in Canterbury are being warned about wild weather impacting road conditions.

Heavy rain in the region has caused surface flooding in many places already.