State Highway 3 between Whanganui and the top of the Whangaehu Hill is closed after a truck crash about 1.40am on Wednesday.
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 are major build-ups of traffic which is being diverted through Durie Hill and Fordell via Warrengate Rd, No 2 Line and Portal St.
New Zealand Transport Agency is warning motorists to expect significant delays at peak times at the intersection of Portal St and State Highway 4 (Anzac Parade).
Motorists travelling towards Whanganui have reported that traffic is backed up to Okoia.
