Kiwi doctors want adults to be banned from smoking in cars containing children.

The ban is already in place in several Australian states. Two years ago Tasmania introduced an on-the-spot fine of $110.

A ban in New Zealand would mean anyone under the age of 18 - the current legal age for smoking - would be classed as a child.

Second-hand smoke inside a car is thought to be just as damaging as a smoky pub - and twice as dangerous when the windows are rolled up.

Members of the Royal Australasian College of Physicians, which represents 9000 physicians and paediatricians in Australia and New Zealand, want to see smokers fined for lighting up in a "confined space" to protect the health of children.

Smokefree Coalition Board chairman Robert Beaglehole agrees.

"Banning smoking in cars is one component of reaching a tobacco-free New Zealand, and we are calling for a legislation for this by 2012," he said.

Beaglehole said the recent success of banning texting and talking on phones in cars - and previously banning smoking in pubs and restaurants - is a clear indication that people are ready for change.

But New Zealand Medical Association chairman Peter Foley said the association would rather "discourage" people from smoking in cars, rather than have it banned.

"It's a no-brainer that smoking contributes to the ill health of other people in the car," said Foley. "It's probably even more dangerous smoking in the car than in the home because it is a confined space.

"But we don't support a nanny state where we have to legislate for everything."