LATEST: Alcohol may have been a factor in a head-on collision on the outskirts of Hamilton last night that has left one woman fighting for her life in Waikato Hospital.
The impact of the crash was so severe it was heard by a teenager wearing headphones and playing loud computer games in a nearby house.
''I knew it had to be bad,'' the teen, who did not wish to be named, said.
''Mum and Dad went straight down, I went to the end of the driveway but I didn't want to go any further - I could hear [the people involved] though - it was pretty awful,'' he said.
Emergency services revealed the crash was one of the worst they had seen.
Two women aged 18 and 19 are both in critical condition in Waikato Hospital's intensive care unit while a 41-year-old woman and a 22-year-old man are both listed as serious in the high dependency unit.
All four patients are from Hamilton.
Waikato road policing manager, Inspector Marcus Lynam, said road and weather conditions were good at the time of the crash on State Highway 23 near Whatawhata about 9.50pm.
"The crash is being investigated by the Waikato serious crash unit however initial indications are the collision involved two cars travelling west towards Raglan and a car heading east towards Hamilton,'' he said.
"It appears the eastbound Nissan Bluebird crossed the centreline and collided head on with a Suzuki Swift car. The driver of a Hyundai Sonata, travelling to Raglan, managed to break and avoid all but a minor impact with the rear of the Swift."
Mr Lynam said Police were awaiting the results of toxicology texts to determine what, if any, part alcohol played in the crash.
Hamilton St John operations team manager Nigel Dawson said the it was of the worst accidents he had witnessed in a long time while Hamilton Police Senior Sergeant Dave Litton was told the scene was ''carnage''.
''It is always very serious when two cars meet head-on,'' Mr Litton said.
Fire fighters took more than an hour to free a severely trapped woman from the wreck, while they spent 30 minutes working on a second extrication.
Mr Lynam said while the Waikato road toll was currently two deaths from two crashes compared to seven deaths for the same period last year, any death or serious injury was an avoidable tragedy.
"We are urging drivers to be mindful of the fatal five; that is speed, alcohol, keeping left, seatbelts and reckless or dangerous driving, if everyone takes care to avoid involvement with each of these factors we will all be driving to survive and ensuring safer journeys for all road users."