Police said State Highway 30 in Awakeri is down to one lane just south of the SH2 intersection following a crash.
It said emergency services were notified that a small number of vehicles had collided with a cow on the highway just before 6.00am.
St John said one person was transported to Whakatāne Hospital in moderate condition.
Fire and Emergency New Zealand said crews from Edgecumbe attended the scene.
Motorists are advised to avoid the area if possible, and expect ongoing delays.
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