Chinese authorities have seized 72 tons of milk powder believed to be tainted with melamine. Another 100 tons still need to be recovered, state media reported.

According to the reports, the tainted powder is thought to originate from a batch recalled after it killed six children in 2008 and made 300,000 ill.

Melamine is a chemical used in the manufacture of plastics and fertilizers that can give food products the appearance of a higher protein content.

On Saturday, authorities closed two dairy companies in the Ningxia Hui autonomous region for selling tainted milk powder.

The Ningxia Tiantian dairy was shut down after it was found to have processed and repackaged over 164 tons of milk powder, according to China Daily. The dairy had received the powder from another company as payment for debt.

The products made from the raw material have been sold to five factories in the Inner Mongolia autonomous region, Fujian and Guangdong provinces, China.org.cn says.

In addition, candies made with tainted milk powder were found in Jilin province yesterday.

So far, only 72 tons of the product have been traced and authorities are trying to track down the rest of the batch.

Another company, Ningxia Panda Dairy, was closed because of its ties to a Shanghai dairy which was closed late last year, the BBC says.

The latest discoveries marked the second batch of tainted milk products found in a 10-day crackdown launched on Monday last week.

Last week, three suspects were detained in Shaanxi province for selling tainted products.

Zhao Shuming, secretary-general of the Ningxia Dairy Industry Association, told China Daily that many small companies did not have the equipment to test for melamine. He also said that some companies would keep tainted products out of stores until the end of the round of intensified inspections.

22 dairy firms implicated in the 2008 scandal were ordered to pay millions of dollars in compensation to the families affected by the incident, the BBC says. Two people were also executed.

Cindy Yang, a dairy analyst for the Netherlands-based Rabobank Group in Shanghai told the Canadian Press that this latest incident is unlikely to damage the industry to the point that the 2008 scandal did.

"These companies are quite small ones," she said, adding that the largest dairies operating in the country implemented stricter safety measures after 2008, and consequently raised the prices of their products.