The warning comes before Waitangi Day - the first to fall on a Monday since 2006, meaning a three-day holiday for many this weekend - with police promising to be visible on southern roads.
Southern district police photographs, which have been released to the Otago Daily Times, show three vehicles - including one towing a boat - crossing double yellow lines.
While each driver was likely to face a fine of $150 and the potential loss of 20 demerit points, their actions put lives at risk, police said.
District road policing acting manager Senior Sergeant Steve Larking said drivers who crossed the centre line "endanger the lives of other road users and represent a real risk".
"Numerous people have been killed or injured through this kind of driving behaviour," he said.
Crossing the centre line was one of the most dangerous things motorists could do.
"It goes without saying that, if you cross the centre line, you are at greater risk of travelling in the path of an oncoming vehicle and causing a serious injury to yourself, your family or other road users."
Motorists who crossed the centre line were often driving too quickly, were distracted or tired, or even affected by alcohol or drugs.
Police have also warned motorists that driving too slowly also presented a risk to other road users, and those who noticed traffic building up behind them should pull over in a safe place to let others pass.
"This means other drivers are less likely to become frustrated and attempt a dangerous or risky passing manoeuvre that could compromise the safety of other road users."
In addition to alcohol checkpoints and speed cameras, police would be enforcing a 4kmh-lower speed tolerance this weekend, he said.
The lower speed tolerance would be extended this month, as February had been identified as a high-risk month in terms of road safety and road toll.
Lowering the speed tolerance during holiday weekends meant fewer deaths and injuries resulting from crashes, he said.
