A Christchurch man's death in a high-speed crash illustrates the "terrible consequences" of choosing to drive at excessive speed while intoxicated, a coroner says.

Kyle Eru O'Brien, 30, was going twice the speed limit and was more than three-and-a-half times over the legal blood alcohol limit when his ute barrel rolled, hit a power pole and broke through a fence on November 16, 2022.

He was also ignoring a court-imposed ban on driving at the time.

That evening he had spent more than three hours drinking at the Yaldhurst Hotel and taken diazepam, which he had not been prescribed, associate coroner Stephen Burdes said.

O'Brien's partner and friends left the hotel about 9.25pm and began driving towards Christchurch in a Mazda, with O'Brien following in his white Mitsubishi ute.

"The vehicles were overtaking other cars using the painted median strip. The Mazda was in front; Mr O'Brien's ute was behind," Burdes said.

One witness cited in the coroner's report estimated O'Brien's ute was about 20 centimetres away as "zoomed past" their car on State Highway 73, while another said it flashed by at "incredible speed".

"I was travelling at or slightly below the posted speed limit which is 60kph. I would estimate the vehicle was driving at 120kph," the witness said.

"All of a sudden after the white vehicle went past me and past the vehicle in front, it appeared to flip onto its side, possibly the driver's side. I do not know what caused the vehicle to flip on its side but I heard a loud bang and scraping sounds."

The crash happened about two kilometres from the hotel, Burdes said.

Police found O'Brien might have swerved sharply to the left to avoid an oncoming vehicle.

Two off-duty police officers who arrived just after the crash found O'Brien trapped in the vehicle with his head resting on the roof, Burdes said.

Fire and Emergency and Hato Hone St John paramedics arrived shortly afterwards to cut O'Brien free and provide first aid - however, he did not recover and was pronounced dead at the scene.

The cause of death was recorded as multiple blunt force injuries and possible respiratory compromise.

Toxicology reports showed O'Brien had a blood alcohol level of 179 milligrams per 100 millilitres of blood, well over the 50 milligram legal limit for a driver in New Zealand aged 20 years or over, Burdes said.

O'Brien had also taken diazepam which could have exacerbated the depressant - or brain-slowing - effects of the alcohol, he said.

Because of previous drink-driving convictions, O'Brien had been banned from driving a year earlier for at least 28 days or until he applied for an alcohol interlock licence, which he had not done.

"I cannot say why the two vehicles were travelling at excessive speed, why they were overtaking other cars along the median strip, or why Mr O'Brien drove while grossly intoxicated (having also consumed diazepam) and while disqualified. All I can say is that Mr O'Brien's decisions that evening led directly to his death," Burdes said.

Burdes said there was little he could add to existing public messaging about the dangers of speeding and impaired driving.

However, he directed the findings be released to the media as an example of where those decisions could lead.