Beijing - A court in northern Chinas Hebei province on Monday tried four people for "endangering public security" after they made melamine-laced protein powder designed as a milk additive, state media said.

The charges are the most serious announced since the health ministry said tainted milk powder was believed to have killed six infants and sickened nearly 300,000 babies earlier this year.

If convicted, the four suspects could be sentenced to at least 10 years in jail or even to death, the official Xinhua news agency reported from the Intermediate People9s Court in the provincial capital of Shijiazhuang.

Another five people were tried on Monday by lower courts in the Shijiazhuang area on the lesser charge of "producing and selling poisonous food", the agency said.

Local courts on Friday tried the first six suspects for producing melamine-tainted protein powder or adding it to milk, but it was not clear if any of them also faced charges of endangering public security.

The Shijiazhuang court on Monday heard charges that the four suspects had produced and sold more than 200 tons of protein powder made from melamine, malt dextrin and whey powder between December 2007 and August 2008.

Prosecutors argued that the protein powder brought "serious damage to the health and life of consumers," which should be considered as endangering public security, the agency said.

The courts did not announce verdicts against the nine defendants on Monday, and no verdicts were reported after the earlier trials on Friday.

The Shijiazhuang court is scheduled to try Tian Wenhua, the former general manager of Sanlu, the dairy producer at the heart of the scandal, on Wednesday on charges of "producing and selling fake or substandard commodities," the agency quoted court sources as saying.

Milk dealers reportedly added melamine-laced protein powder to raw milk that was sold to Shijiazhuang-based Sanlu, which was one of China9s major dairy produce retailers until the scandal broke.

Sanlu was declared bankrupt earlier this week with debts of 1.1 billion yuan (161 million dollars) after ceasing production in September.

Government officials said Sanlu knew about the contamination of milk powder with melamine since March but didn't order a national recall of the powder until September.

Melamine is used as a binding agent and coating for particle, fibre and laminated board in furniture. It is also used to make fertilizer. (dpa)