China's top food safety regulator demanded on Monday a thorough investigation into the whereabouts of 17,000 cans of fake-brand baby formula－which have been sold nationwide－to eliminate risks.

According to the China Food and Drug Administration, quality inspections by police in Shanghai showed that the formula met national standards and posed no safety threat.

The Supreme People's Procuratorate said on its website in March that six people were arrested in Shanghai in January for producing and selling the fake-brand formula, from which they profited by nearly 2 million yuan ($310,000).

The procuratorate said the suspects were accused of buying cheap baby formula, or milk powder, for "non-baby use" and packaging it in cans bearing the labels of top brands.

They then sold the products to salespeople in places including Zhengzhou in Henan province and Xuzhou in Jiangsu province. The salespeople sold them in a number of places across China, the procuratorate said.

The suspects include two alleged organizers, surnamed Chen and Tang, two others thought to have produced baby formula cans with top-brand labels, and two who allegedly supplied low-end milk powder, the procuratorate said. It also said prosecuting agencies in Shanghai are tracing those still at large.

Shanghai People's Procuratorate said on Monday that the case is still being investigated. It declined to give details, such as the brands that were pirated.

Song Liang, an independent dairy analyst, said that due to weaker supervision, sales of fake top-brand baby formula are more widespread in small and medium-sized cities and on private online shops.

"In many cases, milk powder that is almost past its expiration date is repackaged and sold online as imported baby formula," he said.

Such products can evade supervision by authorities as they may have no quality problems and do not cause serious harm to babies, Song said.

The China Food and Drug Administration said on Monday that consumers should be cautious when buying baby formula online.

It said both sellers of the formula and online sales platforms must follow food safety laws, adding that online sales platforms will be held accountable if found to have been involved in food safety crimes.

Zhou Wenting contributed to this story.