The gay community has won a historic victory in achieving legal recognition for same-sex partnerships, but has been stung by a last-minute push against civil unions by Auckland City's mayor.

The same day that Parliament voted 65-55 to pass the legislation, Mayor Dick Hubbard sparked outrage as details were revealed of a letter he had signed urging MPs to oppose the bill on the basis that the children of gay couples were more likely to be victims of abuse and murder.

Auckland gay community representatives say they feel betrayed after Mr Hubbard campaigned in front of the Gay Auckland Business Association, saying he stood for diversity and tolerance.

While campaigning, he quoted American Professor Richard Florida's creativity index that gay and immigrant populations boosted a city's prosperity.

The bill, which polarised public opinion and split political parties, has dominated Parliament for three days, as MPs opposed to it fought to change the bill or force a referendum.

On Monday, Mr Hubbard and his wife, Diana, with Air New Zealand chief executive Ralph Norris, signed a letter to MPs asking them to "do the right thing for our children" on civil unions.

The letter quoted "international research" that children from unions other than marriage were more likely to be abused, murdered, suffer depression, lower educational standards and poverty "than those raised in a traditional heterosexual marriage".

The letter was signed by Mr Norris and his wife, Pam, in a private capacity; John and Alma Sax, of Southpark Corporation Ltd; Ian and Mary Grant, of Parenting with Confidence; Alan Duff, of Books in Homes; and Michael Brown, Pro Vice-Chancellor of Maori at Auckland University.

Mr Norris has twice been named the country's top-performing executive by Deloitte and Management magazine.

Mr Hubbard has found himself out of step with other prominent civic leaders - his deputy, Presbyterian minister Dr Bruce Hucker, supports the bill, as does Waitakere Mayor Bob Harvey and Wellington Mayor Kerry Prendergast.

Dr Hucker was at a rally outside Parliament yesterday declaring the bill "another step towards being an inclusive New Zealand".

Western Bay community board member Bruce Kilmister, who is gay and an HIV-Aids health campaigner, said he was gobsmacked and initially refused to believe Mr Hubbard had signed the letter.

"This flies in the face of everything he purported prior to being elected and immediately alienates a large proportion of the population in this city."

The GayNZ website accused Mr Hubbard of betraying his gay supporters.

Mr Hubbard said yesterday that he was a moral conservative who, like MPs, was entitled to express an opinion on the conscience issue.

He denied flip-flopping on his earlier comments.

"I made it very plain that my position was one of tolerance but not of endorsement and I believe this stand is compatible with that.

"I am very keen on the sanctity of marriage and I'm very concerned that the Civil Union Bill as it is now is very close to the concept of marriage.

"I certainly don't regard myself as homophobic in any shape or form," Mr Hubbard said.

After the bill was passed, he said: "I don't walk away with a sense of disappointment, I just feel it was appropriate to express my views."

Mr Sax said the letter, including his attached submission on the bill, was based on social science.

"I became very concerned that we were losing our focus on what really works for our children. The statistics [in the submission] showed the great divide between heterosexual marriage and everything else, from solo mums, live-in boyfriends, short-term, long-term de facto, gay unions and so on.

"I came to the conclusion it was incredibly wrong not to consider the rights of our children."

Mr Norris declined to comment on his reasons for signing the letter but Alan Duff said no one had asked the question "What about the children?" during the civil union debate.

"It's as simple as that. I'm not homophobic," Mr Duff said.

The final debate in Parliament dwelt on debate over whether the legislation was gay marriage by another name.

One of the bill's architects, Labour MP Tim Barnett, said Parliament would have rejected a proposal to legalise same-sex marriages.

"If that had been the only option available I would have thought it likely not more than a quarter of the MPs would have supported that.

"This option to me is the best outcome."

In Parliament Square, joyful supporters baited stony-faced opponents with the wedding tune Chapel of Love.

The supporters hailed its passage into law as a victory for New Zealanders' sense of fairness, and opponents claimed it was a sad day for New Zealand.

Australian gay activists are following the events, saying the issue highlights their Government's backwardness.

additional reporting: NZPA