One person has been taken to Waikato Hospital following a crash near Whatawhata.
The crash happened on State Highway 23 near the junction of Kakaramea Rd, according to a witness.
The witness, who was travelling with a group of Royal New Zealand Navy officers, said an elderly woman was injured in a crash between a car and a truck and trailer unit which was transporting a digger.
"We were the first on the scene and as members of the navy we all have first aid training so we made sure everyone was alright until the ambulance arrived," he said.
"It was quite a high-impact crash and the car was pretty much T-boned."
He said the crash caused chaos with traffic.
Fire and Emergency confirmed they were called to the two-vehicle collision, where one person was trapped.
"One person was lightly trapped in a vehicle and we had to remove a door," a spokesman said.
A St John spokeswoman said one patient was transported to Waikato Hospital in a serious condition.