China's quality watchdog said here on Sunday that the latest tests on Chinese milk powder found no traces of melamine.

It was the fourth round of tests for the industrial chemical since the breaking 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.

The tests covered 39 batches of baby formula from 10 brands in six provinces and 133 batches of other milk powder from 45 brands in 18 provinces, the agency said.

So far, 499 batches of baby formula from 53 brands and 709 batches of other milk powder from 142 brands produced after Sept. 14 have been tested and none contained melamine, it added.

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