The current affairs show suggested thousands of Aucklanders in the Tongan community were buying the meat. It alleged some sellers of the product appeared to be promoting it as suitable for human consumption.
A spokesman for the New Zealand Food Safety Authority, Dr Geoff Allen, sought a copy of the tape of the show's investigation and told host Mark Sainsbury that an investigation would be undertaken.
Close Up outlined an inquiry by reporter Matt Chisholm into a pet food abattoir in the Counties region selling horse meat for $3 a kilogram.
While the meat is labelled as not fit for human consumption, evidence uncovered by the show, using an actor, indicated the meat was being promoted as suitable for people to eat.
It was also found to be for sale from South Auckland markets. One vendor was cooking horse meat and selling it in a Tongan dish called Loi Hoosi for $5 a serving.
The actor was able to buy 6kg of horse meat directly from the abattoir for $20. He was told that it was fresh and and had been killed only that morning.
At one market, he managed to buy 7kg of horse for petfood for $10.
Tongan Advisory Council chairman Melino Maka estimated that up to 10,000 Tongans in New Zealand - about 20 per cent of the New Zealand Tongan population - ate horse meat, despite them being unable to buy horse meat in the country labelled as fit for human consumption.
He had been aware of the problem of people buying horse petfood for human consumption for three years and had made efforts to stop the trade.
Maka said members of the Tongan community were playing Russian roulette in eating the meat.
He believed in some cases the meat was even being repackaged by some operators and onsold for human consumption.
Dr Allen, of the Food Safety Authority, said offering the likes of pet food as being fit for human consumption would represent a breach of the Animal Products Act. A company could be fined up to $500,000 and an individual up to $100,000.
Dr Allen told Close Up that his agency had been aware of petfood sales at the market and had inquired into the matter at least once before. However, the meat was correctly labelled as unfit for human consumption and legal requirements were being met.
However, the inquiry by Close Up had shown the apparent promotion of the horse meat as suitable for human consumption "which it clearly is not".
The Close Up revelations come at a time when horse meat sales internationally are under greater scrutiny than ever before.
The European Union has announced six-month withholding periods for horses unless they were raised specifically for slaughter for human consumption.
The concern centres on the common use of powerful agents in leisure and competition horses, such as the painkiller phenylbutazone. The withholding period is designed to reduce the likelihood of these agents entering the human food chain.
The tough new EU requirements are expected to deliver a serious blow to the slaughter industries of Canada and Mexico, where most of the horses going to slaughter would not qualify under the new rules unless held for six months beforehand.