Fire Service central communication spokesman Carlos Dempsey said the incident occurred near the Mohaka Viaduct, which spans the Mohaka River.
He said initial reports indicated the vehicle may have plummeted up to 150m off the road.
Fire Service high-angle rescue teams were on their way to the scene from Napier and Hastings.
There are unconfirmed reports that up to three people are dead. But Dempsey was not able to confirm whether there were any fatalities.
The incident happened at about 2.40pm.
A police spokesman confirmed police, fire and ambulance staff were at the scene