'Man up': Jacinda Ardern challenged to protect children from smoking in cars

Public health campaigners have laid down the challenge to Jacinda Ardern - protect our children from smoking in cars.

Figures suggest almost one in five kids are exposed to second-hand smoke in cars every week, an estimated 100,000 kids.

A leading public health professional says a law change is needed to bring us into line with the UK, Australia and the United States.

Appearing on the AM Show on Tuesday, Otago University Professor Richard Edwards said he's frustrated by the lack of action from our MPs and laid down the challenge to the Prime Minister.

"You can do something really tangible to improve the health and future well-being of children," he told The AM Show host Duncan Garner.

"We've got this Smokefree 2025 goal, which is wonderful. But to be honest, since the new Government has come in, not very much has happened to show we're doing things to move towards that.

"And I think this would be a very clear signal that the Government takes this seriously, they want to achieve Smokefree 2025, they want to protect our children, protect their health. And here's a relatively simple way to do that."

But the Prime Minister calls the proposed ban on smoking in cars with children a "secondary measure".

"Of course I have sympathy with the issue - you've heard me talk about it before - but I do keep making that point that even if support is garnered for this one change, that if you're... still smoking in your car that probably tells me that you're still smoking within closed doors of your home and no-one's asking us to do anything there," she says.

"The best thing we can do is try and have families stop smoking altogether and these, I guess, are secondary measures."

Ms Ardern says she wants to see a consensus on the issue as the Government "can't pass things without support".

That's not good enough for GP Dr Lance O'Sullivan, who says the Government should get it right.

"This is a good example actually that one Government can be very much the same as the next," he told Garner.

"It doesn't matter who's in power, they can make the wrong call and they are. They shouldn't be going out and looking for the numbers."

Children's Commissioner Andrew Becroft says New Zealanders need to "take a stand" for our children.

"I think the result so far has been underwhelming and disappointing and the time to act is now and we've got to put a stake in the ground," he told The AM Show.

"I see this as a no-brainer. I mean, the evidence is clear, the medical consequence are serious, it's something we can do, it's a positive step forwards and it is enforceable."

Another backing a law change is Dame Tariana Turia. The former Maori Party co-leader says smoking in cars can be regulated like the ban on cellphones in cars, and a phone line could be set up for anyone who spots it.

However Ms Ardern told Garner enforcement could be difficult.

"This would only ever be as good as the enforcement and look the same issue with people on the phone in their cars, we still rely on a level of enforcement in place, something that I'm sure that overseas jurisdictions could tell us about how it's worked or hasn't worked in other places," she said.

But Prof Edwards disagrees, comparing it to the success of enforcing seatbelt laws.

"I think actual enforcement by and large would look after itself," he says.

"It would just send a very very clear signal that this is not a behaviour that's appropriate and most people will fall into line."

Mr Becroft also says it won't be that difficult for the laws to be policed.

"It's not an onerous burden on the police," he argues. "They're not turning the police into the health police."

And Dr O'Sullivan has a message for Ms Ardern: "Man up, make the right decision and find some courage and do the right thing".