Prime Minister John Key is concerned Chinese reports about a chemical residue found in New Zealand milk powder, linking it to a deadly contaminated milk scandal in 2008, could harm the country's reputation.

It was publicly revealed last week that Fonterra knew about small levels of the dicyandiamide (DCD), used in some fertilisers, had been found in some of its dairy products back in September.

The company did not inform the Ministry for Primary Industries until October - sparking reports of safety concerns in foreign media and accusations of a cover-up.

The Chinese government has sought assurances from New Zealand's ambassador to China, Carl Worker, including an urgent risk assessment report, according to the website of the Chinese Communist Party's official newspaper, the People's Daily.

The level of residue found in the milk powder is reported to have been 100 times lower than European Union limits, and there's been little concern in many countries, including other parts of Asia and the United States.

However, Chinese media reports that the incident brings back "painful collective memories" of the 2008 scandal when formula and milk powder were adulterated with melamine, killing six infants, and leaving about 860 hospitalised.

Prime Minister John Key reiterated on Tuesday that there is nothing to be concerned about.

"At the end of the day, New Zealand has world-class food safety standards. In fact we've spent quite a lot of time with the Chinese government trying to help improve their safety standards for their agricultural sector and other parts of their food production chain," he told reporters at Waitangi.

Mr Key said any misreporting by international media could be damaging to New Zealand's food safety reputation.

"I would be very concerned and fearful of that. That's why we've tried as hard as we can to get the correct information out there and why the Ministry for Primary Industries and the ... government's been talking to (our) counterparts overseas."