Tainted powder was also detected in Jilin province in the northeast, it added.
Melamine is the same substance that killed six babies and left another 300,000 infants ill two years ago.
"The authorities have demanded strict investigations and punishment and the preventing of any problem milk powder entering the market"
Xinhua news agency
The chemical was found in the products of 22 Chinese dairy companies in a massive scandal that also led to huge worldwide recalls of Chinese dairy products in 2008.
Melamine, used to make plastics, fertilisers and concrete, can cause kidney stones, urinary tract infections and death, if ingested.
Its high nitrogen content allows protein levels to appear higher when added to milk or animal feed, allowing traders to disguise substandard products.
A total of 21 people were convicted for their roles in the 2008 scandal, and two were executed last November.
However, the authorities found food products from three companies laced with melamine earlier this year, with dozens of stores in southern Guizhou selling the contaminated products.
Some of the recently seized milk was likely stockpiled instead of destroyed as ordered two years ago, Chinese state media said.
The report did not mention any deaths or illnesses blamed on the latest batches of toxic dairy products, but Xinhua said "the authorities have demanded strict investigations and punishment and the preventing of any problem milk powder entering the market".