A serial sperm donor alleged to have fathered more than 20 children has hit back amid claims that he misled the babies' mothers.

Tauranga man Tony Ross could have fathered 21 children by 16 mothers according to information provided to TVNZ's Sunday programme.

One of his biological children said she just wanted him to stop being a sperm donor, amid unproven allegations that children may be inheriting health defects.

Shortly before the episode aired Ross posted on Facebook that "very hurtful" claims had been made.

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He said he had donated sperm for a decade and often did so two or three times to the same family, he posted.

"There are 4 mothers who have decide they no longer want to update me and for the last 6 months have decide to do as much damage as they can," he posted.

"There [sic] faces are blacked out, very easy to lie then."

Tony Ross says:
Tony Ross says: "There is no New Zealand law that says how many children you can father." Image / TVNZ

The post claimed the signed agreements included photo updates.

"I did file in court for a visitation order, not custody, as they will claim.

"What these mothers are claiming is that I am hereditary heart murmurs, glasses and Asthma.

"I don't wear glasses nor anyone in my family have Asthma apart from the children.

"I have never had a heart murmur and have been checked see attached letter.

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"None of these mothers have done any testing on themselves."

When confronted in Tauranga by TVNZ, Ross insisted he had done nothing wrong.

"There is no New Zealand law that says how many children you can father."

Ross told Sunday the concerned women were "bitter" and wanted to cut him out of the picture after finally conceiving children.

One Wellington couple told the programme they had posted about Ross on an online forum and the response led them to believe he had fathered at least 29 children, many born to same-sex couples.

Another woman, who went by the pseudonym of Ana on the show, said she picked Ross after finding him on a donor website and later had two children using his sperm.

"Obviously two women can't make a baby, that's the science of it," she said.

"We had to go and research other ways on how we could go about this."

Ana said she signed a contract in which Ross waived his parental rights.

But she alleged that as the children grew up, he sought an increasing amount of interaction, including unsupervised contact.

That was ruled out after an expensive court battle but Ross continued to contact the family.

"We are stuck to this man, whether we like it or not for the rest of our days," Ana said.

"It's an actual living nightmare and that's no over exaggeration."