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An attempt to recover a truck that plunged 15m down a bank has been unsuccessful. 

Police arrived at West Coast Rd in Castle Hill shortly after 5am on Wednesday to find the truck had run off the road and had come to a stop among trees on the embankment. 

Waka Kotahi NZ Transport Agency truck crash said the recovery attempt could not be completed in the timeframe. 

They will attempt to recover the truck again from 12.30pm today. The road will be fully closed and the work is expected to go through to about 4.30pm. 

The closure point on the Canterbury side is half a kilometre east of Castle Hill Village, between the village and Thomas River Bridge. 

Electronic signs are advertising the closure. 

Drivers can take the Lewis Pass route (SH7) via Waipara as an alternative slightly longer but fully open route. 

The road was initially closed for several hours on Wednesday. 

"Fortunately, the driver appears to have been uninjured," a police spokesperson said. 

No ambulances were called to the scene. 

By 4.55pm, the road had partially reopened and at 7.15pm, Waka Kotahi said State Highway 73 was open with stop/go signals in operation.