China's quality watchdog said on Sunday no trace of melamine was found in the latest nationwide tests on liquid milk.

It was the 13th round of tests for the industrial chemical since the the report of the tainted baby formula scandal that left at least three infants dead and sickened more than 50,000 others, according to the General Administration of Quality Supervision, Inspection and Quarantine (GAQSIQ).

The tests covered 477 batches of baby formula from 66 brands in 22 cities including Beijing, Shanghai and Tianjin.

The government set temporary melamine content limits in dairy products of a maximum of 1 mg per kg of infant formula and a maximum 2.5 mg per kg for liquid milk, milk powder and food products that contained at least 15 percent milk.

So far, the quality watchdog had conducted sample tests on 6,274 batches of liquid dairy products manufactured after Sept. 14 from 138 brands and found all safely under the limits.

Melamine, often used in the manufacturing of plastics, was added to sub-standard or diluted milk to make the protein levels appear higher.

(Xinhua News Agency October 20, 2008)