State Highway 3 south of Whanganui has re-opened following Wednesday morning's truck crash which caused traffic chaos in the city.

The road was closed for nine hours after emergency services were called to the scene at about 1.40am.

A police spokeswoman said there were no serious injuries reported in the crash which occurred two to three kilometres south of Whanganui near the Lake Wiritoa turnoff.

There were major build-ups of traffic which was being diverted through Durie Hill and Fordell via Warrengate Rd, No 2 Line and Portal St.

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Motorists travelling towards Whanganui reported traffic was backed up as far as Okoia.

New Zealand Transport Agency still advise caution through the area.