The New Zealand Food Safety Authority says it is seeking clarification over media reports out of China that link New Zealand to a Chinese company at the centre of a milk contamination scandal.

Dairy company Fonterra has confirmed it is a supplier to a Chinese infant formula company under investigation over claims its milk powder contains hormones and is causing infant girls to grow breasts.

A Fonterra spokesman confirmed the company supplied milk powder to Synutra International.

"Fonterra is a supplier of milk powder to Synutra International but we understand Synutra sources some milk locally and imports whey powder from Europe."

However, both Fonterra and the NZFSA said hormonal growth promotants were not used on New Zealand milk-producing cows.

"In New Zealand there are strict legislative controls on the use of Hormonal Growth Promotants (HGPs) - they are not allowed to be used on milking cows," Fonterra said in a statement.

The strict controls mean that it was not necessary for New Zealand milk or milk products to be routinely tested, Fonterra said.

A NZFSA spokesperson said the agency had been talking with Fonterra and Chinese authorities to seek clarification on the matter.

"We need to establish whether anything is going on. At this stage we have not had anything concrete, but it seems improbable that it is a New Zealand problem."

Fonterra said it remained 100 per cent confident about the quality of its products.

Synutra's public relations manager Zhang Yingjiu told media yesterday the questionable milk powder was all imported from New Zealand, and had been approved by China's customs before entering the mainland market.

Fonterra also owned a major stake in the Chinese dairy company Sanlu, which was at the centre of the 2008 melamine contamination scandal in which babies died after drinking infant formula.

Chinese dairy products were recalled worldwide after it was found melamine, which is used to make plastics, was widely and illegally added to the products to give the appearance of higher protein.

Melamine was found in the products of 22 Chinese dairy companies in a massive scandal blamed for the deaths of at least six infants and for sickening 300,000 others in China.

Xinhua news agency yesterday reported China's Health Ministry had instructed food safety authorities in Hubei Province to investigate the claims about hormones in the milk powder.

Parents and doctors in Hubei were reported earlier this month voicing fears that milk powder produced by Synutra International Inc, a dairy company set up in east China's Shandong Province, had caused at least three infant girls to develop prematurely.

A fourth case was reported in Beijing.

Synutra also tested the product, so the baby formula was safe for customers, the Synutra manager said.

Also, there was no point in the company adding hormones as that would not add to the product's efficiency, the manager said.

Chinese Health Ministry spokesman Deng Haihua told a press conference yesterday that food safety authorities were already testing samples of milk powder made by Synutra and there was also a medical investigation into the cause of the infants' conditions.

He promised timely publication of the investigation results, Xinhua reported.

He said oestrogen hormones were forbidden in milk powder products. The Ministry of Agriculture had formulated test procedures for oestrogen hormones and had provided them to Hubei authorities.

On its website, Nasdaq-listed Synutra said in a statement that it had never added man-made hormones or any other illegal substances to its milk products, and that all its products were safe.

The statement said it was "unscientific and unreasonable for some media to blame premature puberty on the milk formula".

The company was backed by Yao Hui, deputy head of the endocrine department of Wuhan Children's Hospital, who said three of the four infants treated for the condition at the hospital had never eaten baby formula made by Synutra.

The other baby used to eat Synutra formula, but switched to other brands last year, Yao said.