A ban on importing or selling cars equipped with faulty Takata airbags is in force after the compulsory recall of 50,000 vehicles began yesterday.
The Government refused to extend the 40-day grace period, which ended on May 31, despite car importers asking it to do so.
Takata's older-model Alpha airbags have been associated with 23 deaths globally, although none have been in New Zealand.
They have been known to explode unexpectedly, spraying passengers with shrapnel.
"Because of public safety we wanted to continue with the time frames we put in," Commerce and Consumer Affairs Minister Kris Faafoi said.
"Extending the period for when those imports couldn't come into the country wasn't an option for us."
If affected imports could keep coming into New Zealand it would considerably slow down the process of getting rid of them from our roads, Faafoi said.
Anyone caught knowingly importing affected cars could face penalties, although Customs staff would be able to use discretion in issuing penalties during a two- to three-month grace period where small numbers of cars were imported in genuine error.
"But that would be the exception rather than the rule."
There was also a ban on selling affected cars that hadn't had the airbags switched.
The cost of doing so fell to the car manufacturer and was free for consumers and retailers.
Faafoi announced the recall in early April, which he said gave plenty of time for both used car importers and retailers to comply.
All of the 50,000 affected cars in New Zealand must have their airbags replaced by December next year.
Although he expected to see more airbags replaced in the next few months, keeping momentum going over the 18 months would be a challenge, which the Government needed to rise to, Faafoi said.
"It's a rare thing to have a compulsory recall like this, so the pressure is on us to do it and do it well."
The Takata recall is only the second compulsory recall in New Zealand history, and the largest of cars by far.
It was made compulsory after a voluntary recall had little impact over four years.
Faafoi expected to have a more exact idea of how many cars had had their airbags switched when the first session of a monthly group meeting was held on June 12.
However, anecdotally he'd heard technicians working for the manufacturers responsible for changing switching the airbags out had been very busy since the recall was announced on April 4.
Because some of the cars affected were so old they may not be on the road anymore, Faafoi said 100 per cent compliance was not the goal, but he hoped that in a year the country would be tracking at about 70 per cent.
If it looked like people weren't doing anything, the Government would consider options like failing Warrants of Fitness if the airbags were still installed.
But Faafoi hoped it wouldn't come to that.
"I'd prefer we didn't have to do that, that we have an effective recall process and a large majority can be changed."