The St Johns spokeswoman confirmed they sent one ambulance and another rescue helicopter that transported one person to Waikato Hospital in a serious condition.
At 6.10am this morning police were alerted to a car having slid off the road and into a ditch at or near the intersection of Hururua Rd and SH4.
The driver appeared to be uninjured and advised he did not need roadside assistance.
At the same time, police were alerted to a truck that had rolled blocking the southbound lane on State Highway 4, 1.5km north of Ohutu Rd.
The road is still closed from Whanganui through to Tohunga Junction so the truck and trailer could be removed.