A woman caught driving drunk was allegedly more than six-and-a-half times over the breath alcohol limit.
The 30-year-old woman's driving raised "extreme concerns" by a member of the public who followed her through Richmond, near Nelson, about 6pm on Friday.
She allegedly drove over a traffic island, mounted a kerb onto a footpath, and was slumping at the wheel.
The witness phoned police and followed the woman to her Richmond home.
Sergeant David Lauer of Nelson police said the witness waited outside until officers were there "within minutes".
The woman gave a reading of 1690 micrograms of alcohol per litre of breath -- more than six times the legal limit of 250mcg.
"She was pretty cooperative but she wouldn't tell us where she had come from or how much or what she had had to drink," Mr Lauer said.
The woman, who was the only one in the car, was charged with driving with excess breath/blood alcohol and will appear in court later this month.
Mr Lauer praised the "great work" of the concerned member of public.
In 20 years of policing, and processing hundreds of drink drivers, he had never come across such a high reading.
"There is a lot of traffic on the road at that time of night and a lot of people out and about, so it was very dangerous," Mr Lauer said. "Most people get the drink-drive message and are responsible, but there's always a few people out there who don't have any concerns for other motorists and continue to drink and drive -- they are the ones we want to get off the road."
It was a busy weekend for Tasman District police on the roads.
One driver in Marlborough was charged with dangerous driving after several people reported them to be driving erratically and crossing the centre-line.
A passenger in a following vehicle recorded the driver's actions and guided police to intercept them.
On Sunday evening, a camper van was stopped near Kumara after police received information from other drivers that the vehicle had been crossing the centre-line.
Members of the public who witnessed the driving were also able to provide police with video footage which resulted in the driver receiving an infringement notice.
Tasman District prevention manager Inspector Mat Arnold-Kelly said in each of these incidents, the people who witnessed the dangerous driving did exactly the right thing.
"By calling police immediately and getting evidence on their cell phones they have enabled us to take positive action against these drivers," he said.
"These are great examples of police and the public working together to prevent injury or death on our roads."
By Kurt Bayer of NZME. News Service
