Key Points:

The voices were tense, but there was no violence when supporters from both sides of the smacking debate clashed at Parliament today.

About 400 people marched on Parliament grounds from Civic Square, singing the national anthem and yelling opposition to Green MP Sue Bradford's bill to change the law on smacking.

Meanwhile, an estimated 1000 protestors braved a wet, wintry lunchtime in Christchurch to march from Victoria to Cathedral Square.

The Wellington demonstrators were followed by a small group of about 30, who inside Parliament grounds tried to drown out speakers from National, Family First and ACT, with their chant of "Repeal 59", 59 being the section of the Crimes Act that Ms Bradford wants removed. It allows the statutory defence of justifiable "reasonable force" against assault on a child.

Some of those 30 mingled among those in favour of the law staying as it is and there were angry arguments, but they didn't escalate into anything physical, other than when a man at Civic Square referring repeatedly to Jesus grabbed another man on the leg.

The Bible-carrier had taken offence to a comment from the other man, but it turned out both were from the anti-smacking side of the debate. Police quickly intervened.

The issue clearly has its personal side, with For The Sake Of Our Children Trust campaigner and former Winz chief Christine Rankin telling the crowd, "the childless Prime Minister thinks she knows better than the public", Newstalk ZB reported.

Ms Rankin also took aim at Ms Bradford, saying comments she made last October that men opposed to the bill were sexual perverts who get a kick out of kicking children "says it all."

A repeated theme of the placards and statements of those opposed to the Bradford bill was the interference of "nanny state" in their family lives.

"It's social engineering," yelled Louise Simpson, who said she had travelled from Waitakere in Auckland to take part in the march.

"What they are actually doing is adopting the same fascist ideas as the Nazis and using our police force that we pay for to enforce it."

Ms Simpson said she was disappointed with the stance of Maori Party MPs, who support Ms Bradford, on the bill.

She was one of a number of marchers accompanied by children, with grand-daughter Nikita in tow on a pushchair.

From the other side of the argument, Ella Edginton said she was "disgusted" by the large number of "brainwashed children" brought along to "bulk up their numbers".

But Family First NZ director Bob McCoskrie said there were children, too, among the Bradford bill supporters.

And what did the kids think? Stratford schoolchildren on a camp to Wellington took part and said they were against the Bradford bill, with Scott Caskey, 12, saying: "There is no other way to discipline your kids."

Scott Gilmour, 12, was in his group, but didn't quite agree. "You shouldn't smack your kids because it hurts," he said.

ACT leader Rodney Hide took place in the march, while Wellington deputy mayor Alick Shaw held a placard supporting the bill, which he said had been the subject of "more misrepresentation" on any issue he could remember.

Mr McCoskrie said he was pleased with the turnout, but not so pleased with some of the behind-the-scenes action taking place.

"We are aware of social workers who have been told not to sign this petition (calling for a referendum on the issue) who have been threatened with discipline, so there is a lot of thought control going on in the public service which is sad."

Both sides of the debate agreed about the need to deal with child abuse, "but we have got to get honest about the causes of child abuse rather than this bill which is going to invade every home and treat every parent as a child abuser. That is totally the wrong message."

Wellington police reported they were pleased with behaviour at the "well-organised" march.

Among MPs who accepted the banner were Ms Bradford and her Green Party collegues, five from Labour, and Katherine Rich from National.

In Christchurch, a crowd estimated at up to 1000 protesters marched from Victoria Square to Cathedral Square in pouring rain.

Speakers, including Christchurch radio talkback host Simon Barnett, humourist Gary McCormick and NewstalkZB radio talkback host Ali Jones all spoke against the bill.

Police reported no problems.

In Auckland, Judy Bailey, Paul Holmes, Brian Edwards, Jude Dobson, Linda Clark, Keith Quinn and Bishop Richard Randerson were among those to ink their handprints and add their signatures to a banner supporting the bill.

The banner, "Hands Up for Change!", was handed over to MPs supporting the bill outside the Parliamentary Library this afternoon.

"I really appreciate the courageous stand taken by these people in the public eye, who are well aware of just how contentious this issue has become," Ms Bradford said.

"A lot of misinformation has been circulated and needless fears have been whipped up and I find it very heartening to see that the people who have signed have all concluded that repeal of s59 is something in the best interests of New Zealand children."

Prime Minister Helen Clark earlier confirmed Labour was discussing with other political parties the possibility of introducing Sue Bradford's private member's bill as a Government bill.

That would see the bill go to a vote within days rather than weeks. The move follows Labour's decision to withdraw a bid to have the bill heard under urgency.