A woman accused of attempting to kill her ex-partner in a car crash told a nurse she caused the collision, a jury has been told.

Maxine Avlon Paul, 58, of Waihī is on trial in the Rotorua High Court and has pleaded not guilty to one charge of attempting to murder Mark Marion Bickley and two charges of dangerous driving causing injury in relation to Hamilton couple Ciaran Dunn and Zoe Rothnie.

The charges related to a head-on crash on State Highway 2 about 200m north of the intersection with Aongatete Rd on January 7, 2017.

Bickley, badly injured in a crash, yesterday gave evidence that Paul twice grabbed the steering wheel of his station wagon, the second time sending it into the path of a four-wheel-drive Toyota Surf Hilux.

Bickley said his and Paul's relationship had been "rocky" at the time of the crash.

On a return trip home to Waihī, Paul began arguing with him about his decision not to let her continue drinking with her friends in Whangamatā, Bickley said.

A "grumpy" Paul grabbed the steering wheel and tried to turn the station wagon into the path of a logging truck but he managed to regain control, he said.

A few seconds later, she grabbed the steering wheel again, this time with "a lot more force" and told him she was going to kill them both.

This caused the station wagon to swerve into the other lane and crash into the Hilux, he said.

Crown witness Helen Martelli, a registered nurse, today told the court she was heading to Katikati when she came across the crash and gave Paul and Bickley first aid.

Martelli said Paul, still strapped into the passenger seat, was semi-conscious, bleeding profusely from a wound on her head and was drifting in and out of consciousness.

"When the Māori lady [Paul] regained consciousness her first words were, 'f***, I caused the accident, it was my fault, it was my fault. It was words she repeated several times," Martelli said.

"I also remember her saying, 'I'm so sorry for what I did to those [other] people."

Martelli said she overheard Bickley saying to Paul: "Don't worry darling, we'll worry about that later."

Bickley, who appeared lucid, told her that he and Paul were returning home from an event and both had a "skinful", but his then-partner had caused the crash.

Wendy Foster, a Hamilton teacher, said she had been travelling about 100m behind the station wagon for up to two minutes before it crashed.

Foster said she had seen the vehicle she was following weaving in its lane before the driver appeared to regain control, but a few seconds later, it suddenly "rocketed" across the road.

"I felt so sorry for the oncoming vehicle as there was nothing it could do."

Crash analyst Constable Michael Chelley said he found two sets of distinctive yaw marks on the road which confirmed Bickley's vehicle slid sideways from left to right across the centre line before hitting the Hilux.

To have left these yaw marks and gouges, the station wagon had to be going at between 67km/h to 73km/h at least, he said.

Bickley had claimed he was travelling 60km/h.

Chelley said there were no visible signs of braking on the road before impact.

However, under cross-examination by Paul's lawyer, he conceded there was no way of knowing its exact speed before it crossed the rumble line or at the point of impact.

The trial continues this afternoon.