A collision in Waikato, possibly caused by another vehicle, has left two women fighting for their lives.
Sergeant John Stapleford of the Waikato Highway Patrol said initial indications were that the crash, north of Ohaupo, involved more than just the two cars that collided.
"It appears the driver of a northbound silver Mitsubishi car was passing a van in the northbound lanes of SH3 when an older green Ford Falcon sedan began to follow her very closely.
"As the woman completed her passing manoeuvre she moved into the left hand lane but the driver of the Falcon then cut sharply in front of her, causing the woman to lose control of her car.
"We believe that the Mitsubishi then careered across the centreline, into the path of a southbound Honda car resulting in a collision that left both female drivers suffering critical injuries.''
Mr Stapleford said the green Ford Falcon did not stop and was seen to drive off at speed.
Emergency services were called to the scene, about a kilometre south of the intersection of Airport Rd and SH3, about 4.37pm.
Both drivers, believed to be aged 27 and 72-years-old, were taken to Waikato Hospital by ambulance suffering from critical injuries.
"We don't know for certain that the driver of the Falcon was aware of what occurred, and if that is the case we would ask that person to come forward.
"Traffic on SH3 at the time of the crash was busy and we believe there may be several drivers who saw what happened. If that is the case and you haven't already done so, we ask that you contact police.''
Anyone with any information is asked to contact Mr Stapleford at the Waikato Highway Patrol base on 07 858 6200.
Alternatively information can be left anonymously with Crimestoppers on 0800 555111.