A specialist chemical tanker unit was travelling down from the Bay of Plenty but severe weather on the Desert Road had caused delays, Mr Gillbanks said.
"We are having to proceed with caution as we don't know whether the current leak is just from the overflow or from a much larger rupture that we can't see.
"We need to be certain that if we lift the tanker before it is emptied, that we will not be causing any environmental hazard."
A logging expert was on his way to the scene to remove three trees which had fallen on the tanker.
SH1 at Ohakea remains closed, with a diversion in place.
The accident comes after a head-on crash on State Highway 30, 11km east of Benneydale, about 2pm yesterday which killed four people and injured three.
Those who died included Lucan Ryder, 29, Patricia Matthews, 30, and Monique Ryder, nine, who were all in the same car.
Two other children in the car were injured, police said.
One woman was killed in the other car, and a man was taken to Waikato Hospital.
Police would not name the woman until she was formally identified.
Early this morning, one person died in a three-car crash in Auckland.
The accident happened shortly before 1am on Auckland's southern motorway, about 20 metres north of the Princess Street off-ramp, northern police communications Inspector Shawn Rutene said.
One person died at the scene and two others were taken to hospital.
- NZPA
